I've tried almost everything.

I got a classic t maxx 2.5. I got it in 2007. I have ran in it, 2.5, 2.5r(current engine), 3.3, durtrax .21, sh .21, dynamite .26 mach 2, axial .28, axial .32. I know all this is crazy, but I had to try to see which engine will give me the best performance. The reason I want back to the classic setup because the big block setup did not yield the results I was expecting. The major down side was the blow transmissions I had to replace.
I still have the extended chassis and looking to rebuild with all new parts. If anyone has any advise on what is best, please post all ideas. I will post pics throughout the project.

P.S I have the gearing formula, and have gone through all the gearing setups I could think of. It was the weight of the bigger engines and other parts that were used to improve the weaker parts that slowed the truck down. Can't figure out were I went wrong, but willing to try it again with help this time.