I am not sure how much mileage I am getting out of my truck.... But I found that there is a 12 HP and 4 MPG gain just by putting a DTR sticker on your truck

I have so many on mine now I have to pull over every hundred miles or so and drain some fuel out on the ground

 

Have you checked the timing on either of your 12V's? The first thing I thought when I read your post is that your timing has slipped a little, as they are known to do, and it affected your fuel mileage. I got about 16 out of my 96, in 2005, pulling a 20ft enclosed trailer full of Mom's furniture, and the back of the truck was loaded with junk too. My mileage is suffering a bit now, and my idle is down about 200 RPMs, so I'm thinking my timing has slipped, but I just haven't had a chance to check it yet.

Chris

 

Yeah, I agree that the ULSD busted up the 20's. 16-17 Highway/City now, where it was 3-4 more than that with the LSD. Still WAY better than a gas V8 or a Powerstroke.

 

2 years ago hauled a 2200 lb TC 10K miles all over the north west and averaged 17.5. I left 10 days ago and have covered 3800 miles same TC loaded about the same and have yet to get 17 mostly about 16. no leaks any where now tell me what happened. Truck runs fine cranks just touching the starter. new fuel filter before started trip.

 

Oh no smoke except a little puff when changing gears.

 

we pulled 26 in a 01 5 speed with a quadzilla adrenaline, injectors, s and b intake on running 35s.. the over head console inst always a good thing to trust. figure out zour milage mathematically, but remember, if you have larger tires, your trip odometer reading will be in correct.

 

Stamey it may have slipped on the '98 since it has worse mileage, I know the timing on the '96 is OK as you can tell by the combustion rattle. I had set both to 16 but it's been awhile.

 

This is what I see too. I had gotten 22 at times with mine until ULSD came out. 20 is tough to get now.

 

Nothing has changed truck runs great. same size tires. I am in the Yukon tonight filled up in Fort Nelson BC this morning and happen to notice theirs was .05% max.

 

I run back and forth from Sacramento to Santa Cruz a lot these days and I am on my second 96 12v my first was an automatic with a #3 feul plate and a straight pipe exhasut with high flow air filter and I was always averaging 17.5mpg running at 74 mph at 2000 rpm, my second 96 12v is the 5spd with a #0 feul plate and a straight pipe with higher flowing air filter set up and I run it with about 1000 pounds of tools and other things in the bed and I find I am getting around 20.5mpg at the same rpm but slower speed of 70mph. next test will be to run it at 1750rpm the whole time to see if I can get better or worse milage but I do notice if i run it at lower rpms in the city {like 1000-1250 i know that seems too low} it tends to get way better milage as opposed to running at 2000 {or as close to 2000} on freeway getting best average milage!

 

I got 21 on the highway a few times until the ULSD came out. Now I'm lucky to get 19.

FWIW, my mileage didn't change a bit after the mods.

I just installed an AirDog 150 (replacing a dead Holley Blue pump) and I'm crossing my fingers that it might help a little.

 

21.67 mpg on my last long trip which was a week ago. 2002 2wd quadcab longbed. Its all stock including the auto except for a litttle larger tires, which means I probably got a little better than what I hand calculated. Over 600 miles of that tank was highway with the rest in 1st and 2nd crawling up gravel roads in the hills. I figured if it would of been all hwy it would of cleared 22 easily. I also drove 65 mph religiously on this last tank.

 

Well I run 265/75/16 Michelin ltx and now have 4" cool duals from MBRP just installed. It is making a little more noise and seems to run better. When I take off I don`t baby the truck. I was told by a pro truck driver to get it up to speed in lock up as soon as you can for the best fuel mileage. I will be going again sun for another trip with the fiver and will check the mileage and see if the big exhaust will make a difference. Most of the trip I wont see much over 55 mph speed limit. its way to crocked and hilly to go faster than that. I lost mpg with the 10 torque plate but have a lot better truck that don`t lose as much speed on the hills like it did stock.