Pulling the same aero shape trailer, I get the very same MPG from a Toyota 5.7 V8 as I did with a Honda 3.5 V6, at the simlar speeds. For a time I thought I was down a bit with the V8, but its practically dead nuts the same range of high 8-11mpg (even 12 on rare occasions) depending on conditions and speed.
Towing lesser trailers back in the day with 4.3 Vortecs provided...you guessed it...the very same MPG I see today.
Non-towing, the Toyota V8 is not known for getting over 18mpg highway, while I could get 22-24 with the Honda V6. This does not appear to be the same situation you have with the truck options you are considering. Go with the V8.
