Captian, did you by chance put the gearbox build guide that Durango posted a link to to use? Here it is again.
http://www.team-durango.com/blog/?p=2584 I bought my Rango used from a friend at the track. A couple gears were chewed up and the car sounded like a chain saw. When rebuilding the car found my friend had not taken all the "slack" out of the bevel gear(imput shaft). I have a couple weeks on the car now with no problems. I too think the problem was the bevel gear. Also the set screw for the bevel gear gear needs to be good and tight with the proper amount of loctite. Good luck!
Joseph.