My rear Diff gears keep stripping out. I've replaced them 2 times. I have a 1/16 E-Revo running 3S Lipo with the speed gear I belive its the 23. I only run the car on the street is there an upgraded rear diff I can purchase or should I shim the stock one when I reaplace the gears. If I have to shim it what are the part numbers and how many do I need? Thanks for your help.