I will get 17-18 hiway at 75 with no trailer in tow, if I am pulling ANY trailer from a small utility to my 29 foot rv my mileage will drop to 8-11. I am not very inpressed with my towing mileage. Power is great.

I am running 285/75/16 and have had GM reproram the system, also a K&N air filter, and a supper chip programer. I can set the programer on any setting and it will not effect my mileage.

I have 25k miles on the truck.
is this nomal mileage for this truck?

2007.5 LMM