I started out years ago towing our 7,000 lb trailer with my old chevy 2500 with the 350. I tow mostly in the Sierra and Rocky Mts. I hated the way I had to slow down to 45 mph going up the grades. So ...
Most folks are afraid to let the V-10 do what it does best and that is to generate horsepower and torque with RPM. On most of the recent V-10's you get max torque {420#), at around 3,200 and max HP {305}, around 4,400.
You are not going to hurt the V-10 by letting it run from 3 to 4 thousand rpm. You will only see those rpm for brief periods on long steep grades. Yep, you will burn a little more fuel but it will get the job done. Put your foot down and go.