5.3 crew with 3.42 gears
With stock tires during commute from work.
With slightly larger coopers on the same commute
I haven't recalibrated the speedometer yet.
On cold mornings my truck is getting around 15mpg to work. Tire pressure starts at around 32 psi. On the trip back with warmer temps and tire pressure back up to 35-36 I'm getting 18-18.5. Seems like the lower pressure and colder air hurts the mpg a good bit.
Also you have to keep in mind I'm running 275 60s without changing the speedo.