This forum always gets questions similar to this, and quite often the (guy who is the) Thread Starter, omits which transmission, and differential gears, the truck has. Thats info that we need. You said it is a Flex Fuel. Did you recently start running E85? Whst gas are you running? It took me long time to figure out that some fuels simply have more BTUs per gallon than others, because some fuels consistsntly get better mpg than others. If you have 3.21 final gears, 70-75 mph in hi gear, is a tall order for that Pentastar, which needs RPM to produce power. If you do have the 3.21/8 combo, why not just avoid 8th gear. Leave it in 7th, so the Pentastar has some RPM to work with. A Petal Commander will make your truck feel more responsive. I pull trailers for UPS for a living. What direction the wind is blowing makes a big difference. These trucks are about as aerodynamic as a dehumidifier.