Hey Rootar.
I've had the very same problem with my E Revo. I'm Positive I had it shimmed right the first time. But when I opened it up after I heard it skipping teeth like that, I found the bearing closest to the pinion gear was really sloppy.
Check your bearings. As a temporary fix, I swapped the pinion bearings around, and shimmed it up tighter. It worked for awhile, but now it's doing it again. I've jumped it a few times, but this thing accelerates HARD!
I'm waiting on some Ceramic Nitride bearings to come in for it. I've heard they are alot tougher than regular ball bearings. It might be something for you to check into.
