I used to get 21+ in my RCSB cruising 75-80mph on the highway(90%highway mileage). It had and still has 30"+ tall tires and 3.42 gears. Lately I can't get over 18 though. It dropped last winter and never recovered for some reason, never figured that one out.

 

I Get 14.8 Driving Very Slow Beacuse I Got Aa Tiket Last Time So Now I Drive Slo I Used To Get About 10 But Know Is 14.8.

 

I travel to Mich. 4 times a yr. and its 400mi. non stop highway at 70/75mph all the way. We average 17.5 mpg with 4 people in truck. That is with 3.73
gears and 17" tires. See mods in sig..

 

17in tire!!!!!!!!! What do the daytons look like

 

Mine is a little weird... I average around 17-18 driving 75. When I bump it up to 85, I get 19-20. The only thing I can figure out is that at 85, the engine is in it's powerband and is running more effecient. BTW, I have 3.42s and I average 20K miles a year. Most are on the interstate.

 

On a full tank of gas which is a 26 gallon tank I went from Virginia Beach, Va to Bristol, Pa which is 298 miles according to yahoo drining directions(just for the mileage info) I made it there on less than half of a tank on a average speed of 70 mph (if I go any faster my wife bi%$hes at me) It takes 5 hours. So 298mi/13gal = You do the math

 

5.3 / 3.73's, im running about 75-80 on the highway and pull down 16 MPG's consistently. On a 30 inch or so tall tire.

Hoping for improvement with my wait4me tune.

 

I once got 23mpg on the highway in my 2500HD - 6.0 LQ4, 4L80E, 4x4, 4.10's, all stock except for a dead transfer case . Amazed the crap out of me, especially since right after that in strictly city driving I got 10mpg . Who knows, my trucks a freak sometimes .

Tom