Speaking of exhaust brake....I have a 2013 2500HD Duramax and the exhaust brake does little to nothing, at least that I can notice. My dealer says it's normal that if there were a problem, it would trip a code. I pull a 5th wheel and was a little disappointed with the exhaust brake. It really doesn't seem to do much. The only thing I notice is that it might downshift a little more with it on.
I set my trailer brakes at 4.5. I think the trailer brakes should be an "assist" rather than do the most of the braking on my rig.