Brake and ABS light on, Rear brakes drag

I have a 93 F350 Dually, 4 door, 7.3ID non-turbo. 98860.00 on the odometer (yes this is a real number ). Brakes completely overhauled 12K ago (new master, new rear wheel cylinders, one front caliper, new pads, new shoes). Went to Wahsington DC and back to Fort Lauderdale no problems. Now after about 10 months, I have a weird problem that I hope someone can give me some words of wisdom....

After about 6 miles or 20 minutes of driving, brakes working fine, the brake light and abs light comes on. The brakes seem to work okay, but they do feel like it takes a little more pressure to stop. About every thrid or fourth time this happens, the rear brakes are slow to release after a complete stop...that is to say, when I am a light and let off the brake, it takes a few seconds for the brakes to completely release. Every once in a while the rear brakes simply drag noticabley, but each time I was close to home, so I would turn the truck off and in the morining all was well....until next time. Obviously, thisis not a good thing.

Things come to mind such as a brake line seperating and bubbling out on the inside and holding pressure or a problem with the abs itself. Anyway, at the risk of replacing parts until the problem stops, I thought I would see if any of you can lead me in a better direction.

Thanks! /ubbthreads/images/graemlins/shrug.gif