My spedo and odometer are off but when i correct for it I get about 275 miles out of a tank in warmer weather, i have an 18 gallon tank and usually fill up with 16 gallons or a little less than that. If i ran the tank dry i might be able to pull off closer to 300 but my low fuel light comes on perty early and the tank looks low on the gage so i fill it up. Right now in the winter months i am getting about 225-250 miles to a tank. I have a V6 manual tranny with 35in tires and 4.10 stock gears.
I use my GPS to get my mpg since it has a program for this in it and gets a more accurate mileage/speed reading than my gauges do since I'm on 33s with stock gears. Last time I filled up I got 14.8 mostly city driving.