I don't own a T-Maxx or have any experience with one, but I do read a lot of posts in this forum and one engine that keeps popping up as a good replacement engine for the T-Maxx is the Sirio .18. Big assed wheelies I think are the order of the day.
Also the OFNA hyper .21 is good but I'm not sure what mods are required. I'm pretty sure the Sirio is a straight replacement.