Suspect a sticking parking brake cable. If no other brake work has been done when this problem started, try flexing the cable in the casing in front of the wheel. You can also try pulling down on the cable in front of the casing, then watching to see if it retracts by itself. If flexing the casing stops the problem, suspect a rusty cable. Over adjustment will do this too.
If the cable doesn't appear to be the cause, remove the brake drum and look at the shoes. Both of them must be against the large anchor pin on the top. If they are, look at the parking brake strut rod between the two shoes. You should be able to push it at least 1/16" to compress the anti-rattle spring. If either of these are not correct, they will cause grabbing brakes. The parking brake cable is still the likely cause, but grossly under-adjusted brakes can cause this condition too if the automatic adjuster cable is broken. You would also notice a lower than normal brake pedal.
Look for contamination from axle grease, and a disconnected or rusted link from the rear axle to the height-sensing proportioning valve.
If work was recently done to the brakes, suspect the wrong shoes in the wrong locations. The shoe towards the front of the truck must be a lot shorter than the one towards the rear.
If this only happens during the first stop of the day, especially on dirt roads, it could be normal rust buildup on the drums overnight from humidity in the air. Not much you can do about that.
Monday, March 30th, 2009 AT 3:15 AM