I've heard of the slipper clutch bushing and bearing problem but that is a fairly easy fix. http://monster.traxxas.com/showthrea...slipper+clutch and http://monster.traxxas.com/showthrea...lipper+bearing

Since you've only had the truck 3 weeks you might call Traxxas and see if they will send you replacements. A quick search of the Traxxas 4x4 forum show others that are having bearing problems. Not necessarily the rear diff bearings.

Also, here is a video on how to clean rubber sealed bearings. http://www.youtube.com/watch?v=T_yhucQjFBg