Agree, it's a tire pressure issue.. Even when the alignment is perfect, tires with lots of rubber tread (thickness) and a deep tread pattern like the Revo, can "squirm" if underinflated (too much flexing of the tire carcass that sometimes causes a twisting motion of each indivdual tread block at the outer edges of the tire, as they make contact with the road surface)and will start to cause cupping.. Sometimes the tire carcass can develop an outright "resonance" or vibration in the above motion, that will definitely cup the tires.. More air pressure to stiffen up the tire can take this out..

I began to see a bit on the front of mine and took the front pressure up from about 33psi to 36 and the wear pattern evened out.. I run 34psi at the back based on very close observation of the wear patterns.

Putting a strip of masking tape across the thread and very carefully pulling onto (and off) the roadway with minimum turning so you don't scrub the tape off immediately, then driving about 15 miles on a level straight road will give you a quick picture of the tire wear pattern. I've used this to tweak both alignment and tire pressure..