you have to get the gap between the gears rite to get the gears to mesh properly. the best way to do this is to put a piece of paper between the clutch bell and spur gear when you push the gears together. dont just push the gears hard together.
i know how the set the mesh i done it on all my other nitro r/c s and they all work fine its just the stampede even i put it on the floor and try to push it it wont move i check the brake and that not stuck could it be a bad tranny