how to fix engine throttle air sensor to normal

I have toyota innova car, engine 2KD-FTV diesel D4D. I bring the car into service of periodic maintenance but prior to that the engine works normal, as usual filter replacement of air filter, fuel filter, i saw technician put fuel treatment into the fuel tank and after service i found the idle is 750rpm with little vibration.I tried to run in highway and i found out 2500 to 300 rpm to have a speed of 100 kph.Its seems that the engine accelerate more but no enough power to run. i also observed fuel consumption become bigger. I already back to service technician and they don't do anything. I go home frustrated.