orolla doesn't pick up good, Power Loss and high fuel consumption

I have corolla 2013, 150xxx KM milage have below issues:

- Car starts well, picks up speed after brakes applied to stop the car the next pick doesn't look good the rpm goes above the normal range and the gear changes a bit late(not all the time, I can say for sure that transmission has an issue)

- Works fine in High Ways with high speed, when speed comes below 20 KMPH it doesn't pick the Speed correctly and kind of lagging or power loss happens.

- Average Fuel Consumption is around 10.8 L/100 KM, I drive mostly inside the city.

Checked with 2 mechanics both suggested changing Spark Plugs, Clean Throttle body, Air Filter etc. I did all the things but still, there is the problem.