Why is it people don't seem to understand the fundimentals of power/weight/aerodynamics/drivetrain and how that applies to gas mileage? It's not rocket science...and if it were, you'd need a much bigger gas tank.
People (and you know who you are), any motor can only get so much power out of a drop of gasoline no matter how well that drop is introduced into the cylinder.
More engine displacement or power from a set displacement (usually) = more gas. More weight (usually) = more gas. Bad areodynamics (usually) = more gas. Drivetrain with agressive fat tires (not to mention 4WD, usually) = more gas.
Put them all together.... = LOTS MORE GAS.
35 mpg trucks that run *only* on gasoline and can go 100+ mph are not coming anytime soon....and very possibly not ever.