I've taken teeth off of 2 spur gears from landing on the rear end, so I got a tbr rear bumper to help with that. Might be a good investment for you too.
As for the slipper, with the truck on the ground, grab one rear wheel with one hand, and put the base of your transmitter on the other rear wheel with enough pressure to hold it from moving, and ease on the throttle. The front of the truck should lift a couple of inches before the slipper slips. So if it doesn't slip, loosen it 1/4 of a turn and try again. Just don't do it to many times in a row, it'll heat up the slipper clutch fast. And check the motor temps to. You can set it a little looser then this, but if it slips a lot while driving, it'll heat up and deform the spur gear.
How are you setting the gear mesh? Many people say to use a peice of paper, but to me, that's a little much for 48p gears. For 32p it's fine, but with 48p I go a little tighter then the paper method. Just a little wiggle is all that's needed.