APT wrote:
Good explanation, parker.rowe. While I understand the math well, my point is that 10-15% more wheel torque may not be enough for OP's exact situation, and even less likely worth $2-3k. 5th gear to 4th gear ratio is 0.85->1.15, plus the 500rpm jump closer to peak torque of the 6.0L. That's free, a button click M5->M4.
I'm with intheburbs. Let it rip. The powertrain is 2500HD designed for far more abuse than recreational RV towing.
I agree. That 6.0 will turn 3k or more all day long, and that was the OP's original question.
Just watch your temps and let'er eat!