Reduced top speed and lowered mpg

[scorpion9856a]

I bought my PCX 125 2019 in August 2023, at that time, its top speed was 67 mph and it used to do 28 miles/litre, but now for last couple of months, its top speed is down to 59 mph and it is doing 25.7 miles per litre even after changing roller and belt, clutch plate and rear tyre. I have told mechanic several times but he does not care or may be does not know the cause. Can some one suggest the reason....?

[Conelite]

How many miles are on the Bike? Did he replace the rollers with stock weight or go heavier/lighter?

As for the MPG. If you are getting 25.7MPL/116MPG, I would not be complaining. Thats incredible. Loss of 10mpg when you used to get 127 is not a lot. That can change between fill ups just by being more aggressive on the throttle. lol Im guessing he went lighter with the rollers, which would hurt your Top speed and lower your MPG since the engine revs higher.