Interesting set of events.
After coming to a stop then accelerating, the front end of the truck began to pull to the right. Stopping even at 5 mph engaged the anti-lock and worsened the pull. I had the car looked over by a GM dealer and by an experienced friend both of whom told me the "Anti-Lock Brake Pressure Monitor/Modulator Valve" was causing the all 4 of the brakes to seize. I tried resetting the calipers and took out the abs program (big mistake with a 100 foot hill for a driveway), which made the problem worse totally locking the front wheels.

I prefer to do the work myself and prefer using Delco parts. My knowledge is really limited on trucks so any advice, or things to look out for while working would be greatly appreciated. Many thanks.

 

I would try replacing the part recommended by two knowledgeable people. Bleeding an ABS system is a little different than a conventional omer.