1997 Suburban bent axles?

3,000 mile ago I had new rear drums and brakes installed. After driving My 1997 Suburban 1500 for about 1400 miles, the rear brakes seemed to be grabbing/pulsating when the brakes were applied. Took it back to the installer, they checked it out and said the rear drums were out of round and turned them. They also checked the front and said it was in excellent shape. About 1500 mile later, felt same grabbing/pulling. Took it back, was told drums out of round again and they won't honor because they believe it is a "driving style" issue causing the drums to heat up. Truck has only 60,000 miles and have not had the problem before? Took to the dealer yesterday, they said yep, rear drums out of round, but the mechanic also believes the rear axles (both) are bent and adding to the problem. Truck never in a collision, no damage to rear rims due to hitting a curb or anything? How can I tell if rear axles are bent? Willing to spend money to fix, but don't want to play the guessing game?