I need help deciding on gearing

[RED TAHOE LS]

I'm getting about 15 mpg combined give/take

Jeremy, with a lot of experience in RV's including motorhomes, T trailers, pop-up campers, you can through the above statement you made out the window. Towing 3400 box is not like a vehicle which is more streamlined and aerodynamic. The box tends to trap a lot of air between the two vehicles. 8 to 10 miles is it and you gotta plan for just the slightest grade and hills because you loose your speed quick. My coach was 38' with 460 ford EFI, 4 speed with OD, and it did not take me long to realize when to use the OD button.
Your Tahoe is well equipped with enough power if you use it wisely. I would agree going to 3:73 gears would be of no gain, and the 4:10 would be great with the next larger tire you mentioned. Good luck.
David g.......​

 

[Upper tanker]

Thanks for the input guys. David, I know that any fuel "economy" gets thrown away when towing anything. When towing, I don't really care what mileage I'm getting. However, I do drive this thing on occasion or when my beater breaks down, so I'd like to retain mid-teens. I will go ahead with the 4.10s and see how it works.

Cheers!