Rear brakes dragging on one side 2003 gmc 2500hd 4x4 seems to be after brakes were crowded harder than normal

Tim, I'm not sure if you have rear disc or drum brakes, but this is usually a caliper or brake cylinder (at the wheel) problem. If you have drum brakes, check for any problems like broken springs on the shoes, which would result in parts floating around, and brakes not releasing properly. The same for disc brakes, make sure nothing has become loose (mounting pins for caliper). If you find it is a brake cyl/caliper problem, you will need to rebuild or replace it. Make sure you bleed the brakes for the entire system (you want to flush out the system to prevent further problems), as old brake fluid can become contaminated (brake fluid absorbs water, which corrodes calipers and brake cylinders, leading to failure of those components). Last, make sure it isn't a parking brake that is not releasing. Parking brake cables corrode from exposure to the elements and can bind up, causing the brakes to drag. Use something like WD-40 on the cables to keep them operating correctly.