Originally Posted by mikennrg
Aerodynamics will have a bigger effect on highway MPG than any other mods you can do. Things like bed covers, mirror deletes, blocking off more grill, aero under trays, reducing ride height, reducing wheel well gap are all drops of rain. But many drops of rain can result in a puddle.
Guys are noticing MPG increases from the Diablo and Bullydog tuner. I think the added power makes it easier for the truck to stay in MDS mode. Eliminating the clutch driven fan while adding a 180 thermostat then setting the e fan temp to 200 degrees can help on the highway. If you're not running A/C the fan will never come on while moving.
I agree with much of this. Even with the A/C on while moving at highway speeds, it's unlikely the electric fan will come on. Messing with the cat is a bad idea, IMO. One - because I've never seen any imperical evidence that there's any mileage to be gained and two - it will kill your warranty.