I'm going to say they'd be different. Yes, 'gain' is 'gain', but we must factor in the differences in how the T.V. interprets those numbers. Also, does the trailer have standard, self adjusting or hydraulic brakes? Are the brakes drum or disk?
Our 5r has self adjusting brakes. Weighs 12,000 loaded and I have the controller set at 'Heavy Electric' with a gain of 4.5
You don't show if you have a gasser or diesel. Also if your son's GMC is a gasser or diesel. If you have the Cummins and he has gas, there is absolutely 0 comparison between the two. Even if he has a diesel, there's still a big difference between the two because of our Exhaust Brake and Tow Haul combination.