My Rally has ground to a halt each time it's been run in decomposed granite or soft dirt. Opening up the underside reveals little rocks and other pulverized stuff getting in through various openings in the underbelly skid and under the motor.
I have no doubts about the power of the VXL motor as it's literally lathed sections out of the center drives.
A secondary issue is dust and dirt working its way into the rear diff housing (this was only a couple offroad sessions after a full rebuild).
Solution: some self adhesive foam rubber weatherstripping to block off the openings; up front around the transmission output and aft near the rear diff input shaft.
Seems to be working...