Should I use cruise control while towing a travel trailer

I do when it is flat. I have a Ford powerstroke diesel - it has plenty of power going up pretty significant grades. However, if I don't manually lay off of the accelerator going up hills, it will max out the turbo psi, and I think I can see the gas gauge physically moving. I have found in hilly areas with the cruise on 60-65, I will get as low as 8 mpg. Through the same stretches laying off the pedal but not to the point of slowing way down (maybe drop to 55 on big grades) I can get closer to 12 mpg.