Ugh mines all scrwed up some1 help me!
 

Ok so i was messing around with my xmods and i had stage 2 drift motor with soft tires and whenever i would turn the tires had a way of slipping off the wheel so i well, glued the tires on the wheel so i could drift like mad. Shortly after this my car started going REALLY REALLY SLOW but the motor was doing max revs. When i got my car off the ground and turned one of the wheels the other wheel didnt turn which means something is slipping differential wise. So today i bought the AWD kit cuz it comes with another back differential. I put it in and well still doesnt fricking work, tried over and over added grease everything it just is fricked up.

Any ideas im desperate.

Heres what I do when I have a problem like that.

I start at one end of the driveline, motor pinion is a good place to start by making sure it doesnt slip and closely look and test each part untill I find the slipping/broken part.
You dont have to take the whole car apart (then again you might) you just have to verify each piece.

and also check if there is any hair or dirt

if you got ball bearings make sure one of them didnt sieze. that happend to me yesterday. i would take the whole rear end out and thoroly clean everything to make sure.