Good discussion. I suspect our weight difference could be part of the issue. My 2015 364TS GVWR is 22,000 and I tow a 4300lb (empty) Jeep Liberty. (In the previous scenario, we were on I-75.) A significant added problem is torque "decay". Once you start losing speed, it takes X amount of ft/lbs torque to stop the speed reduction (decay), and an additional amount of torque to attempt to gain back any of the lost speed...thus the 5K rpm. Ordinarily, increasing speed on flat ground should only take a moderate increase in rpm, but a hill accelerates the need for added rpm. Of course, on flat ground, a "lead foot" can have the same effect. IMHO, on a hill, there are two choices: kick it up to 5K or live with the slower speed. Thank you for the great exchange of ideas.
2015 GT 364TSF