2003 gmc 1500hd 6.0 gas mileage?

got a 03 gmc 1500 hd with 6.0 61,000 miles

how do i get better mileage out of this thing? avg not towwing 11.5
best ever 12.2mpg
worst pulling my car trailer and hauling suburban 50 miles 5.2mpg!!!!

now i've had many fords and gms, but this 6.0 is bad for mileage!

what does everyone else get on these 6.0 for mileage?

I also on a 1500HD w/ the 6.0. Have owned the truck for 5years now and my mileage has been right in line with what yours is getting. I think one time I averaged 13.5 but typically its between 10-11avg not towing.

The only things I've really done is a K/N intake, flowmaster exhaust, and hypertech tuner. None of these products changed the mileage one bit, and if they did it was a very minimal change. I wouldn't recommend any of these "bolt on" deals, waste of money in long run actually. I've accepeted that this is as good as the mileage will get, if you find anything that helps pass it along though. Seems like with these newer trucks the mileage they get stock from the factory is about as good as you can get.

I have a 2005 2500HD extended cab with the 6.0 automatic and 4.10 gearing. I get 11-12 around town and I have gotten as high as 15 on the highway empty. If you try to push it beyond 65 mph the mileage will drop off. I have headers, catback exhaust, tuner, and air cleaner system and none of them improved the mileage even though it sounds great and runs good.