Disc brakes resist fading unlike the drum brakes of 20 years ago. Best to avoid sitting on the brakes going down a grade in the first place and to adjust the trailer brake control and use grade control with the transmission. I bought a 4,000 lb trailer and drove down a 8 mile section of road where the elevation decreased by 3,000 feet and had no need to use the brakes the entire time. However, with the Ram 1500 trucks they are not designed for "heavy towing" in hilly areas and the manual recommends not using cruise control to limit the speed and so you are left with using manual gear select.
Fortunately 4,000 lbs is not a lot for a pickup truck, even a 1500 class one, and it comes down to learning to use the transmission and trailer brakes to control speed on a downgrade. Much safer to have the weight of the trailer being managed by the trailer's brakes than trying to use the tow vehicle's brakes (that is when jackknifes can occur).