I drove my 98 from Ohio to Jackson Hole, stayed for 2 months, and then returned. Here is some fuel data and some pics of the car. The trip out I recorded almost every mileage for each fill up.
1: 272 miles with ~1 gal. left
2: 252 miles with 1.5 gal. left
3: 266 miles with 1.5 gal. left
4: 251 miles with 1.5 gal. left
5: 271 miles
6: 300 miles with 2 gal. left
Note: There were 2 different drivers and these are not all the fill ups because my Dad couldn't remember to restart the trip odometer every time.

I lived in Jackson Hole and put approximately 1500 miles on the car while there. The average mileage per tank was roughly 340. The speed limits are mainly 45 and 55 mph and are strictly enforced. Most of the driving was 5th gear at these speeds or 5 over the limit.

The return trip we averaged 280 miles per tank.

 

Awesome bro. Thanks for sharing. I live a couple hours from the black hills. Cool place, so is jackson hole.

 

Looks like a fun trip. My parents are in yellowstone right now camping somewhere different each day. That would be a fun tirp in an R. Thanks for sharing!