How can you improve rolling horsepower/torque? I'm using the 6.2 gasser, not the truck in my sig.

I just towed my work trailer 2000 miles, it's a v-nose 18' trailer weighing about 10k loaded.

I use manual shift mode to keep the motor from shifting all the time.

Running 70 mph, I could not maintain speed in 6th gear on level ground. 100% throttle would only get me about 65mph.

In 5th gear, I could go 70 on flat ground at 2,000 rpm but any hill or wind would cause me to slow down, so, I had to shift to 4th on every hill to maintain 70mph. Some longer hills would drop my speed below 60 so I then had to run the hill in 3rd gear at 4-5000 rpm.

This drives me batty. How can I get better power so I can run a hill in 5th gear and keep my speed above 65mph? My max speed on level ground in 5th gear was only about 74, that's all it would do.....