I just replaced the planetary gear diffs with MIP ball diffs in our (my son and I) two Rustler VXL's. Traxxas support does not recommend the Traxxas Ball Dif Pro for VXL setups. We ran into problems with the MIP assembly on one. The nylock nut is thick and can cause issues. You have to be very careful to make sure that the female outdrive is less than a full thread engaged from the nylock or you will jamb against the small thrust bearing assembly and not be able to fully tighten the dif. If you can get a 4-40 thin nylock nut instead. If it spins for a run or two you'll groove the thrust plates and flat the balls. The thrust plates are not keyed. This is non-standard for all ball diffs and a concern of this design. You will need to back the slipper clutch one full turn from tight or you will spin the diff. There is absolutely no chance of wheelies with this setup but the posi-traction on loose dirt/wet grass is worth the sacrifice. If you're racing, it is far superior to the planetary dif. I've tried thick tacky grease in the planetary dif but it just moves out of the way after a couple of runs and it's right back to spinning out. On pavement, it is fine as long as you ramp up the throttle. We've seen around 12 runs per vehicle and they're holding up good so far. I guess we'll see how long they last. I still have two planetary difs to fall back on. Also, the last line of the instructions say to tighten the dif all the way, then back out 1 full turn. This is way to loose for our Rustler VXLs, even on 7.2V 6 cell packs. I have one 1/4 turn back and the other fully tight (that's the one we had the problem with). We run NiMH 6 and 7 cell packs. Hope this helps.