Any one else own 91 4x4 2500 Suburban with a 5.7?

Just scored a 91 4 wheel drive Suburban (3/4 ton)with a 5.7. The truck has full Rancho suspension and 4.11 gears with 35in tall tires. The truck runs real good, it has tri-y headers and a custom single exhaust w/cat all the way back and exits behind the rear tire on the passenger side.The truck is very comfortable and really fun to drive. Not to mention it just looks bitchen.We are fixin to take it on a 500 mile trip and I was wondering if anyone else has a similar setup and what kind of mileage you get? Thanks-Ed