I recently returned from a trip towing my 8000 pound 5th wheel w/ my stock '03 HO Dually w/ 6spd manual transmission.
My real question follows the narrative just below.
One day I was climbing 6% slopes at 10,000ft elevation (80degF) in 4th gear no sweat and 1/4th throttle, and the next day...
2003 H.O, 5.9, 3500 Dually, 6spd Manual
On a recent trip towing my 8000 pound RV, I lost considerable power on an uphill section (narrow, 2 lane road) to where I only topped the hill in 1st gear (6spd manual) at 2900rpm w/ the pedal to the floor. VERY scary since there was a cliff on one side...