My '05 5.7 Ram, going by the trip computer(LOL) hold at 14.1 combination in town and some highway. I suspect it's more like 12-13 the way I use the pedal.
Maybe if we could always drive down hill, with no stop signs or lights, and with the wind we could get another two or three!

 

It has a lot to do with how you use the "go" pedal. I've noticed that if I keep it at 60mph or less, I get decent mileage (for a truck) but the faster I go, the fuel mileage really starts to fall off pretty bad.

 

I had a heavy bed cover (tonneau) on mine which I removed last weekend and gained 4 miles to the gallon! Yes, 4 miles to the gallon. . . .amazing.

 

was going to my friends last weekend, filled up and got right on turnpike, set cruise at 60 and didn't touch gas or brake for 45 miles, pulled into his driveway and overhead display read 20.2 mpg, around town i usually get 12 to 13, filled up this weekend got on turnpike set cruise for 75 and got 16.5

 

That cover must have weighed a couple of tons and was a vertical slab.

 

I watched a Mythbusters show on improving MPG. They tried tonneau covers, Cab high shells, tail gate down, and no changes. The best mileage was with no changes others actually lost mpg. Go Figure. The bottom line was speed.

 

Forget those overhead displays....they don't call them lie-o-meters for nothing. If you want better mileage buy a fourth generation and you can actually get a true 20+ mpg on the interstate. The 3rd generations, and I've had both 3rd and 4th, are only going to do so much and 12-14 in town and 14-17 on the road is just about it, and there is nothing you can do to improve those numbers noticeably. The 4th have better MDS system and better transmissions and with those two things they are capable of better mileage. I can set my 14 quad cab on 70 mph and it will give me a true hand calculated 20+ mpg. No computer upgrade, no exhaust upgrade no nothing is going to give you noticeable hand calculated improvements on a 3rd gen