Hello everyone,
Not sure if the truck in question is Drum/Drum or Disc/Drum
I have seen this problem repeatedly with trucks that have 4 drum brakes.
Problem is: Pump, pump, pump.
Solution is: Adjust your front and rear brakes shoes out until you have a light drag on the shoes. (Do this with the tire on), and test drive on an empty street afterwards, sometimes they like to pull right or left with fresh shoes on front drums. Re-adjust accordling to get even braking at all four wheels.
I have seen this problem on disc/drum also.
Solution is: do a full bleed of all four wheels. Adjust rear shoes for correct drag.
If you still have a problem, check your rubber brake hoses, or the seals on the calipers. Look for leaks. Also check proportioning valve, make sure its not sticking to one side or the other.
If all else fails, continue to ask questions at a rapid pace, something will eventually work
Two-bit