I'm getting around 18 to 20 hand calculated. I have bigger tires and a power adder. This is a mix of city and highway driving. I have gotten about 22 on the highway before, but that was keeping it right at 65, which is hard to do.
To be honest with you, I wouldn't switch to a diesel just for mpg. Diesel costs a bit more, so the extra few mpg's you get just about averages out. Plus your paying more for the engine and the maintenance costs a lot more as well. I have had mine since new, and diesel was much cheaper than gas at that point. If I were to get one now, I would not bother with diesel. Or wait a few years until the diesel half tons come out. Maybe the mpg/cost ratio will be better. I was actually thinking of selling mine to buy a gas truck. The newer ones get just about the same mpg as my diesel does. Of coarse if you tow a lot maybe the diesel is the better option.
Chris