I have a 07 RCSB with a 5.7 engine. My truck is a sport package so it has the 4.10 axle ratio and no tow package.
I have 14k miles on the truck and the only mods are a Magnaflow RV muffler and the upper filter removed from the factory aircleaner box.
I felt I was getting better fuel mileage that I expected, way better than the 04 Ram hemi that this truck replaced. Friday morning I had to make a 150 mile trip with several stops and mostly on state highways with little traffic and rolling hills. The outside temp was mid 80s and I filled up with 89 octane Chevron fuel to the top of the filler neck so that you could not put any more fuel in at all. I reset my trip odo and started my trip. Mostly highway driving with little traffic and using the cruise control set at either 60 or 65 mph. I noticed that I had driven over 70 miles before the fuel guage even moved down to the full mark and when I got back to the starting point with exactly 150 miles on the odo the fuel guage was halfway between the full and 3/4 full mark so I knew it would not take much fuel to refill the tank. Using the same station and pump I refilled the tank to the same point where it would hold no more fuel and I was looking at fuel standing in the filler neck that could not go down so I knew the tank was full and could not hold any more. The pump read 5.54 gallons. I could not get another drop in the tank. DO THE MATH! I get 27.075 mpg! Bear in mind the engine rpm was running at or below 1500 rpm all the way. A/C was ON.
I found this hard to believe but I know the facts and there can be no mistake. I do run Mobile 1 full synthetic oil for what good that might do. I do have a hard bed cover also.
Tuesday morning I will make a 50 mile trip mostly highway and I will try this again.
Has anyone gotten even close to this mileage in a Tundra even if you have a V6 much less a 5.7 V8?