ABS control module
 

The rear brakes on my truck are tending to lock up easier and easier with no load. My research seems to indicate that the ABS control module needs replacement or overhaul. Tried to buy a rebuilt module, but nobody carries them any more. New modules are over $800 !!!!!!!! There are places that will overhaul my module if I send it to them, but that will mean that my truck is out of commission until I get the module back and cannot afford the downtime.
What is involved in a module rebuild? Is this something that I can do myself?
Any suggestions as to where to obtain an overhauled module? Any other suggestions?
Are brakes considered part of the drivetrain?
Thanks.