mmgt 3.0 diff problems
 

So this is my first nitro car, and I am new at this. First off I bought a rtr kit, and out of the box it was missing one of the drive cup studs/screw. I found that out after my front differential blew out (broke teeth off the gears). call TA and they replaced it, I got it up and running again, and it was running good, about 4 tanks threw and now my rear differential is blown out., I haven't even begun to dissassemble it yet, but I am wondering why it is doing this, I haven't been hard on it, i mean I have just been running it around on my gravel drive way. I jumped it up my hill maybe 1 foot off the ground, like 2 x's, I mean that is the most minor jump, I wouldn't even call it a jump more like hitting a bump, not at full speed, also It doesn't seem to go into 2nd gear at all, I know it did before, but now just goes really high rpm's and I don't hear it shifting.
Do I need to shim the diff. better? How many shims should I put in? how do you know if you have shimmed it properly?
getting frustrated here

RE: mmgt 3.0 diff problems
 

I would get in T A face and get a new truck sent to you. just a thought.