It sounds to me like your brake shoes are adjusted too tight.
If your brakes seem to work fine first thing in the morning, or when the truck is cold, but then as you drive it you get less and less pedal travel and the brakes start to drag until they lock up, your brakes are probably too tight at the wheels. When this happens you will feel a lot of heat at the wheels. Your brakes are heating up causing the brake fluid to expand.
Adjusting the master when the brakes are hot wont help because when the truck cools, your pedal travel will increase until the pedal hits the floor.
I hope this helps, but I would still do some more research on residual valves.
