[RichardJ]

>> if I ease up on the pedal from a complete stop so that the truck inches forward, I can get a "stutter-squeal<<

Are you absolutely sure the sound is coming from the rear? Have you had someone in the pass seat verify, with window up/down, the sound is from the rear?

Easing up on the pedal at a stop may be allowing the metering valve to hold back the pressure to the front disc brakes allowing the front rotors to roll slightly until the rear can take complete control of braking.
The Metering valve in the combination valve may have a threshold pressure of 50-80 psi., depending on combination valve specs Any pressure below that means only the rear brakes will be engaged.