I have a 2021 AT4 and have the same problem. The 1500 while touted as a great tow vehicle has no electronic or exhaust braking - thus it just rolls very nicely forever and you get to melt your brakes even on flat surfaces. Very disappointed and my dealer has no answers. Oh, they do offer a $3K brake upgrade so you can go about a mile further on a steep mountain decent until they melt. That should help, not.
I called bankspower.com and according the engineer I talked to they have no plans to offer a unit for the 3.0L. From what I can tell there is no brake option for the 1500. Ridiculous. I do understand how to use the manual shifting to lock out upper gears... this has little effect, it just causes higher RPM but little to no braking because a diesel does not have a throttle like a gas engine - just fuel injectors.