I have no idea how the ABS systems work on the modern brakes, but when they first started using them they would release the brakes a bit to prevent a wheel lock up. Now that they have added a computer, and the system is tied to all 4 wheels, its not out of the realm of possibilities they have adapted the the brake system to apply more braking to wheels that the system has determined has more traction and can use more braking. If that is the case, as that system gets older, its possible the mechanical part of the system isn't functioning as well as it did when it was new. The older systems were just bypassed when they no longer functioned the way they were designed to. Can't really do that with the modern system without a major rework.

It would be interesting to hear from the experts how the modern ABS systems work and see if that system could be your problem. Then suggest ideas on where to begin to address the issue. If it is indeed an aging problem with the system, its going to become a bigger issue as this stuff gets older.

Its also likely many others have experienced the same issue you are having, but have been unable to cure the problem and have given up and are just using the truck knowing the problem is there. Some people probably have no idea dragging brakes are not normal. I believe many of the trucks of this era are no longer in good enough condition that many of the owners don't want to invest the money into new parts that isn't solving the problem. They have thrown enough money at it that has not fixed it, they are just going to deal with it the best they can.