If you're not impressed with the acceleration of the T-Maxx 2.5 then there's something wrong. Mine will flip over backwards from a standstill if I want it to.
First thing to check is your slipper clutch. I run mine all the way tght then back it off 1/4 - 1/2 turn.
The next thing to do is tune the engine. Tuning is an art and can be frustrating so take your time and learn how to do it right.
Here's a link to Traxas' instructions on tuning.
http://www.traxxas.com/support/index...l&cat=34&id=92
And here are a couple of videos that are really helpful. They're done on a Savage 25 but almost all nitro engines tune the same.
http://www.youtube.com/watch?v=oSmMzpZM_As
http://www.youtube.com/watch?v=BJFsJAxNoRg
Good luck