I can get 16-17 mpg on the highway, about 12 around town....10 pulling my 6000 lb 5th wheel

 

I own a 1997 c1500 with the 5,7l engine. I'm always getting around 16,5 mpg with around 80% of that being highway driving

 

A 95 did not have the vortec motor so there is a degrease in economy over the 96-98. Also the gear ratio makes a big difference in mpg

 

The rear gear ratio as you said would make all the difference. I had a 98 with a towing package which I drove 800-1,000 per week. Never pulled a trailer just liked the way the truck looked and performed and I think it had a 3:73 or so gearing and nearly all the miles were highway miles chunk it got around 16.8 MPG.
I had 106.000 miles on the original UniRoyal Tigerpaw tires that came on it and still had the original brake pads and shoes on it when I traded it in.

 

My 97 has performance mods, and I get about what poncho62 gets. 16.5 highway, about 12.5 in town. I think the tank size is around 25 gallons, or so. I had a 93 long wheel base before this, and it had a 32, 0r 34 gallon tank, and I think the Suburbans have a big tank like that too. I thought about swapping tanks, but I get about 325 miles to the tank on the highway before a refuel, so for me that's enough.

 

1999 K1500 Suburban, 5.7 vortec Automatic, 30(32?) gal. tank.
I get about 10 mpg around town, and I'm always around town. Course a Burb weighs another half a truck more than a pickup, so....

 

I drive a '97 GMC Suburban C1500 w/ 292,000 miles so far, & I get 13 city driving, closer to 15 iv the highway. That # is pretty steady so far as I've had it over a year now.