I was facing same problem from past 6 months and tried a lot many things but no resuts. Even the top speed on Motorway was restricted to 95 -100 kmph on O/D off and fuel consumption dropped to 7.3 kmpl. So, finally yesterday I replaced my car's gearbox believe me now I am experiencing the same old pick-up and top speed. The whole gear box costs me 20k and I sold my old one in 7ks.
I hope this will help you.