I've been reading around a lot and have tried most of the little tricks to improve mileage but nothing has worked. I got the truck with 92,000 miles on it and it now has 103,xxx and love it other than it's killing me one tank at a time. It's a 04.5 4x4 four door LB 6spd and I've replaced the cat with a magnaflow muffler and the stock muffler with a Aeroturbine XL. I'm running 285/70s at 65psi front and 55 rear when empty and have a smarty jr currently set on tow mode. I cruise between 1800 and 1900 rpm, usually on cruise control. I can't get over 18mpg and normally get 17, with a few tanks lately down around 16 or even lower. It's my daily driver, about 12 miles one way through rolling hills with a 30-45 minute drive at least once a tank. I tow a one car trailer 30 miles at a time maybe once or twice a tank but it hasn't affected a full tank compared to some tanks with no towing. It goes through about a quart of oil between changes and runs like a champ but this seems like pretty shoddy mileage for a properly running truck. My '98.5 would get 19-19.5 without trying and I could get over 20 if I thought about it a little under the same conditions.

Any thoughts of what to do/try? Or is this just how it is?

edit: none of the mods has changed the mileage significantly, I would get the same when I first got the truck.

 

For the truck having the 600 and not the 555highoutput your fuel mileage isnt bad for your driving style. Also keep in mind there is people that kinda dream some numbers up when they bloat on here. if your not towing you should try to advance your programmer up some and see what that does and also are you running a upgraded air intake?

 

The intake is stock but if I get some free time I'm going to cut a hole and run some tube down to get cold air as many have done on here. I also want to get an intake pipe (CFM+ or similar) since the biggest gains they got were right at the rpm I spend most of my time at. I tried the smarty on tow with bumped timing but it smoked pretty badly (fun for a little but annoying after a while) and I've tried it on mileage with and without bumped timing but haven't put any serious miles with those settings. I'll play with them a little and see what happens.