Super newb, eh? What color is your cape?

First, $150 seems a bit steep for a used T-Maxx, but is somewhat reasonable since it came with a .18TM, aluminum upgrades, etc...

Second, if that transmission still has reverse, that's likely what broke. When going to a higher power engine, a Foward Only Conversion (FOC) is very much recommended. If that's the case, purchasing the FOC will get your tranny operating again, and is fairly inexpensive ($11.69 at Tower Hobbies http://www3.towerhobbies.com/cgi-bin...?&I=LXMJG1&P=7)

Post up some pictures, and we can tell you exactly what model T Maxx you have.