Does V6 or V8 produce better FE while towing?

[LarryJ]

i'm looking to trade in my V6 2003 tundra for a V8 4WD of about the same year, but wondering about FE while towing. A year ago I parked the truck and now it's used mainly for towing a 14ft boat on interstate (maybe 750lbs total boat, motor and trailer). I might get 13mpg while towing now. Would a V8 4wd provide any significantly better mileage than a V6 4wd of the same model while towing? The v6 comes in a manual that gives slightly better epa mileage, whereas the v8 only comes in automatic.