I have a 08 Tundra Double Cab with the 5.7L V8 and I drive about 50K miles a year with my job. I have a Snug Top bed cover on mine and I get 20.6 with my cruise locked at 70. I have seen 21 if I lock my cruise at 60 mph. The 4.7L does not get as mileage as the 5.7 because the 5.7L shifts more.

I must be in one of those moods today. Come on and be realistic. When a guy asks for an mpg he wants reality not the 100 mile stretch on the freeway with the wind at your back. A 5.7 gas engine is not averaging 20 mpg consistently, especially not with a 4.3 rear end.

I have a 6.0L with 4.10 rear end and I can hit mid 20's for spurts with active fuel management. I average 15.9 all around with the 6.0L Vortec Max. Put a 2500lb plus boat on any 5.3 - 6.0 gas engine from any make and you will be hitting single digits up to mid teens depending on how you drive.