Look for "hardened" or "heavy duty" gears from any of the makers the previous posters mention. I used HB lightning a few years ago and haven't touched them since. I also upgraded to cnc'd diff cups. Plastic cups were flexing under load and eating gears. Spiral cut ring/pinion works well too. You're pushing a 15+ lb aluminum hunk of a truck around, shit happs until it's fully bombproof. I've got a similar setup I haven't had to fix in a long time.