Sorry for the delay got the truck back,this afternoon, he said that the motor and pinion gear was slipping under pressure? Adjusted the motor a little. Did not help. Runs great on pavement, dirt and really short grass. Even runs good in tall (about 3") grass if I do not start off from a dead start. I can run slow, fast and even almost pop a wheelie in it. As long as i do not start off from a dead start in grass it runs great. It like there is no power when I go and try run it from grass. I can go give it a little bit of a shove then it goes ok. This was not like this when i bought the truck new (about it about a week or so ago). I am to point of putting all the plastic back on and see what happens. I made a statement that i took the diff apart, i only took the case apart. You guys are great and I hope I can get this resolved.
Thank you

Update, I took the driveshaft out making it a 2 wheel drive. No difference. Most of the time it moved on its on, a couple of times I had to give it a push. If I try to make it go and it doesn't ( I keep pulling trigger) it kicks out either the servo or the speed controller I believe. I shut it off and turn it back on and its ok. It does not make any sound or wierd noisies, Everthing is on the initial start, if starts moving everthing is good.