i have a rc10gt with a brand new ae .15 motor and it doesnt seem to go the tires spin when you lift it off of the ground but it doesnt go when you set it down and give it gas any help would be appreciated.
Most likely your diff is loose. You can look in the manual and see how to tighten it. Very simple. If you can't find it, pm me and I'll tell you exactly how.
Here's a forum dedicated solely to the gt: GT forums