Where is yer cabin filter located? I know in my T-100...if I drop the glove box door down I git massive airflow. Not sure if you can do that in the Tundra or not.
One of the factors that most might be overlooking is the amount of rake you have. When I was done with my 5000 mile trip, I was loaded about 400 extra pounds than I would normally be setup with. I got the best gas mileage I ever got with that. I'm attributing that to some of the aero mods but I'm thinking the final squat down on the back might have helped that a bit.
