Just bought a 99 Z71, badly in need of tires. Seemed to get good mileage, about 17-18. I really don't want to give up several miles per gallon for the 285's. Anybody have personal experience with this swap and how it affected your mileage. Not sure what gear the truck has in it,, no towing package from the factory so I assume one of the slightly lower gears wouldn't have been ordered either. Also, anybody got a set of the factory Z-71 Chevy, not gmc, alloy wheels they wanna get rid of? Truck has 16x8 Eagle alloys wheels on it, but I like the factory wheels.

285's will rarely hurt your gas mileage.... Before i put headers on, exhaust, K&N fipk, i got 12mpg with 285's... I got 12mpg with 265's. I currently get 17mpg. I would get 285's. You will be happy with that decision. It will not lower your gas mileage more than 1mpg (26 miles or so)

I just went to 285's and it hasn't hurt my mileage a bit.

Call dealers, if you find the right dealer you can get a set of factory wheels/tires for $400 or under. Its really easy to find them with highway tires, so if you just want the wheels you'll be set. Just don't be thrown off by the few dealers that want to charge $1000 for a take-off set. I found a couple places with small highway tires on stock rims for only $200!

And fill out your profile! Where do u live?

I have a set of stock Z71 alloys and a set of Steel wheels that I want to get rid of cheap. They have been sitting on the back porch at my parents for a year and they want them out of there. The alloys are stock (16X7) and the steel are 16X6 I think. If anyone needs some let me know. The steel are the Scottsdale model with all of the caps and bezel thingy.

ahh hell, my z-71 with an "abused" 350 and 285s got 16-17 on the highway. yours should be that or better.
my 4X4 with a tired 4.3L turning 35"s gets 14.7MPG and thast cheapy gas. with shell and highway miles i get a shade over 15. so dont worry about going up an inch or two