99 Silverado 2500 gas mileage?

Just picked up a 99 2500 Silverado 4x4 extended cab. Just curious to see what folks get for mileage on a tank of gas. I got about 170miles to a quarter of tank left on my first fill with some cold weather warm ups and a little bit of snow plowing. I just had some of the fluids changed (trans,differentials,transfer case) and there is only 54kmi on the truck. Today my SES light came on and the code came back to the 02 sensor not outputing. $$$ is a little tight right now and I had a load on the truck today when it happened so I'm kinda hoping that I won't have to replace the sensors right now, but if the mileage is way off compared to having good sensors then I will definentaly change them. Any feedback would be appreciated!

Forgot to mention its the 6.0 liter. Probably would help.

weak 02 sensors kill your gas mileage, on a fine tuned 6.0L highway driving you should average 15ish mpg, someday invest in a k&n air filter, worth the money. as far as mpg for snow plowing, sorry bud, wont be good. but the power is nice. vrroomm

A lot depends on your gear ratio, gt3 (3.73) or gt4(4.10)s. My 2500 running at 2000 on the tach with 3.73s I get a little over 16mpg, and with midgrade I get a little over 18mpg on the hiway. You can find your gear ratio by looking inside your jocky box cover and looking at the build codes. They are in alphabetical order. Hope this helps so you can do what ever accordingly!

i had to replace both down stream o2's on my truck it made a world of difference power wise and fuel wise i was only getting 10 mpg, now im just trying to squeeze every bit of mileage possible out of that pig, ive got a S&B intake, shorty headers, dual exhaust, bully dog downloader and a throttle body spacer, any ideas on what else fuel mileage wise, with my 33's on it runnin high test im gettin about 15