check for loose hoses and vacuum leaks, use dish soap and water in a spray bottle while the car is running and spray all the rubber hoses, if one bubbles, the spot it bubbles from is a vacuum leak, or you can use carb cleaner (make sure it says flammable on it, if not it wont work) and spray the hoses and if the engine revs when you spray a hose, the hose has a leak. I have the same car you do mine is a 2011 (your maybe a different year) but same engine, I have an automatic and it does feel sluggish when first accelerating as it is just stubborn to shift, the manuals obviously don't have this issue (I drove a few test driving, bought used had to settle for the auto because it was a great deal and in the best shape of all of them I was looking at) if you look near your throttle body on the drivers side of the engine (where the air intake hose meets the engine) you will see 2 hoses attached with square clips, the blue clip hose is a perfect one to do a seafoam treatment on, do this with a warmed up engine, what you do is take the hose off where it meets the engine (just slide the clip up and wiggle off its easy) then get you a 3/8th Inner Diameter hose about 1-2 foot long and slide it on the flange that the other hose came off, then start your car, it will idle bad don't worry about it, you created a vacuum leak but its not permanent get your bottle of seafoam and open it, and tilt it where the hose can barely suck fluid out of the can (the vacuum will pull it out at a slight tilt) you want to be sure its not just getting seafoam fluid it needs to suck some air to keep the engine running so don't dunk the hose in the can, let it suck 1/2-2/3 the can down then stop the car reconnect the disconnected hose and wait about 1-2 hours and go drive it hard, at first it will be hard to start as it tries to compress the seafoam trapped in the cylinders and it will put out a giant plume of white smoke from the exhaust, all normal the smoke will get less and less as you drive try to go above 45mph at a good pace and drive until the smoke stops, then drive more after to clear it all, pour the rest of the seafoam in your gas tank. this will vclean out any stubborn carbon build up and sludge holding the engine back, I do this every 10k miles and I get 30 US miles per US gallon regularly which is phenominal for this car which is only rated at 29 highway. and like you I drive 80mph+ on the freeway a lot and still get excellent mpg.
if it is an auto check the condition of the fluids if it is not light red-clear red and smells burnt then you will want to consult a trained good transmission shop as to how to proceed in changing the fluids, once they get black sludgy or burnt smelling there is internal damage to the transmission 9 out of 10 times because it was either not changed or over heated too many times (auto trannys in these models are known for this, so change your fluid every 15-30k in the tranny (its easy to do a drain and fill while doing the oil, the tranny drain pan is right behind the control arms) and has a drain plug which doing this gets about half the old fluid out so if you do it often you will have decently fresh fluid all the time. the transmissions are not bad they just run warm so they abuse the fluids, but mazda does not specify a change interval just if it looks bad change it which is stupid on an automatic 30-60k is the absolute max you want to run auto tranny fluid. if the transmission shop recommends fluid replacement have them drop the pan and replace the filter in the transmission while its there about 100k is good for tranny filter replacements if you keep the fluids good all the time. I changed my fluid when I bought the car it was at 61k miles (yours is 99k miles converting km to miles) and it does shift better afterwards, though it still needs prodding to downshift so I use manual mode a lot so I can get moving quicker then it wants to decide what to do. though sometimes it shifts great other times it doesn't want to down shift when I poke the gas pedal to get more power in passing situations or it upshifts too early and I am laboring the engine,just the nature of automatics they all do that (many newer ones like on the skyactiv models and newer cars are much faster and shift at better times but ours is still old fashioned, so its not having a problem just running on older tech) using manual mode allows you to keep it in the gear you want and shift when you know you need to.
is the check engine light on? if so have the codes read this will most likely point you in the right direction to look for the issue, if you get the codes read post the numbers back here so we can help you. usa obd2 codes read like p0301 which p0301 is a misfire on cylinder 1 you being in a km country (not stated where) the eobd or whatever is in your country may read different but still post them.
check the air intake hose for rips as this can cause sluggish performance as well, get some mass air flow cleaner and clean the mass airflow sensor per directions (DO NOT TOUCH ANYTHING TO THE WIRES IN THE SENSOR OR IT WILL RUIN IT, JUST SPRAY THE SPRAY ON THEM) this is the sensor near your air filer between the air filter box and air intake hose. cant hurt to change the air filter while your at it as well.
use throttle body cleaner and clean the throttle body (take the air intake hose off the engine side and you will see a gold plate, push it open with your fingers, since we have electric throttle bodies you cant easily do it with the car running to open it up, and running the car with no air filter is horrible for it so don't try. spray a bunch in and let it sit a while then go drive again (it maybe hard to start on this again, its normal) at 99,000 miles your spark plus where do for replacement 25k miles ago so just change them even if your sure the last guy did, just do it, IT CANT HURT and helps eliminate one more thing. use NGK laser iridium plugs (they do cost a bit but are the oem plugs and the only ones gapped correctly for our cars) you need a socket wrench a medium length extension and a 5/8th spark plug socket to change them, oh and an 8mm socket to remove the coils and a 15mm socket to remove the plastic hold down things for the engine cover (they sit on top of the stud 2 of the coils use so they must be removed to do this) this link is to the plugs to use:ILTR 6A 8G / ILTR6A8G | 3787 (x4) / ILTR6A8G (x4) / ILTR 6A 8G (x4) | 3787 / 3787 | Set Of 4 Mazda Speed 3 6 Spark Plugs NGK Laser Iridium ILTR6A8G | New-Part.com
when you say your only getting 370km which approx. equals 229 miles out of a tank of gas, is this filling from when the gas light comes on to full then only 229 miles later the gas light is on again? or do you fill from about 1/4 tank? if at about a 1/4 tank this is close to normal I typically get 240-280 miles out of 3/4 a tank of gas but I do a lot of driving for my job and its mostly freeway cruising at 75-80mph (where 5th gear in the auto on the 2.5 is most fuel efficient) I average 26.2mpg since I bought the car but since doing the tune up and changing tires and a few other things I get 27-30 almost 31 average now. I drive probably 65-75% or more freeway or highway at constant speed a lot I your in town between red lights and stopping and going a lot the mpg in this car is horrible I get about 20-24mpg if I am in a city a lot (mpg is miles per gallon)
try all this stuff and see if it helps, none of it will hurt it can only help, and at worse you got a cleaner or newer part out of it. report back any check engine codes if you have any this can help us further assist.
and I don't know which octane method your county uses sounds like the opposite one the USA and most north America uses but use regular grade(look in your owners manual it should say which grade is recommended, here its 87 octane) fuel not premium, premium is harder to combust and does nothing to help our car (since the 2.5L has no turbo and is only moderate compression) using premium can actually lower your fuel economy noticeably I ran it in mine for a wile to see and it got 1-3mpg less each tank then on mid or regular grade in the usa the lowest common available is 87 octane mid grade is usually 89 and high is either 91 or 93 octane depending on where your at in the country
we use this method for octane here:Anti-Knock Index (AKI) or (R+M)/2 so (RON+MON)/2 just RON or:Research Octane Number (RON) is what most European pumps display. which gives a falsity that using 93 there is better than 93 here (as an example) Because of the 8 to 12 octane number difference between RON and MON, the AKI shown in Canada and the United States is 4 to 6 octane numbers lower than elsewhere in the world for the same fuel. This difference between RON and MON is known as the fuel's Sensitivity MON is: Motor Octane Number (MON) Use the grade specified by your manual you don't need to go higher there is no benefit more on octane ratings:https://en.wikipedia.org/wiki/Octane_rating
so 87 grade gas here(recommended fuel for the 2.5l in the usa) is 93-95 grade in Europe. and if your country uses the RON rating only then you using 98 will net you lower mpg, you may not notice any difference but the car will as it tries to ignite the fuel/air mixture and has a harder time doing so, which results in higher los of energy converted to heat and a less efficient car. the difference in our 87 and 93 in these cars is noticeable but wont cause any major harm to the car if used, just mainly lower mpg because it has to work a bit harder and that working harder is way less efficient then not as it will heat up more and have to pump a bit more coolant and oil fast to keep cool and this will cause energy to be lost as heat and as mechanical losses as your pumps for the cooling and lubricating fluids will be working a tad harder.