Hello, I know that I am new here and the terms performance and fuel economy dont go well together but Im in a bit of a pickle. To start with
I own a 2003 GMC Sierra 1500 ECSB 2wd with towing package and 3.73 gears. My truck has a K&N filter, dual exhaust, MSD 8.8 wires and irridium plugs. All of this is less than 3 months old.

The issue Im having is I average about 14.0mpg. If I do highway driving its worse even at 70mph only turning 1950rpms. My truck came with 305/40/22 wheels on it when I bought it. The guy said he was getting 375miles on a tank in city. I thought that was good, but if Im lucky I can squeeze 180miles on the half mark. I have been keeping reciepts and dividing gallons of fuel used to fill up divided by miles to that specific tank.

My best to date has been 14.8mpg. I would really like to keep this truck but if the fuel mileage stays the same I will have to consider selling it for a more fuel efficient truck.

I have the window sticker for it when sold new and city mpg was rated at 16. Is that correct? If I found a set of stock wheels to put on the truck would my mileage pickup from 14 to 16?

Thanks in advance!

 

is the computer programmed for the size tire you have?

 

I believe if your computer isnt adjusted for the larger wheels it will not accurately read how many miles you have actually gone. Therefore not giving you an accurate MPG reading.

 

a 305/40 on a 22" wheel would total out to be about 31.5" tall (overall diameter)

if someone knows the stock size, then you could find the difference. if it's withing an inch or two, that's not really going to affect fuel mileage at all.

the big problem with oversized wheels is that they're a lot heavier than stock rollers. this could be the reason you're not getting desirable fuel economy.

also, do you have a tune for your truck?

 

im willing to bet with lighter wheels you could pick up that 2mpg.
Stock size is 30.5 so the are bot alot taller

 

Im also betting he has 3.42's turning those 31.5's not to mention 22's are Heavy. but your foot also plays a part in it. The width of the 305's also create more rolling resistance, which lowers the economy more.
I barely touch mine, but when I do you can really see my mileage go down. One to two WOT romps and ive moved at least a line or two.

a lower gear would help a little.

But on my stock 265's, and full bolt-ons im turning out 18-20 city and 23-24 highway.

Its crazy. 250-300 miles at the halfway mark on a Z71...but, im really waiting to see how my new wheels and tires will affect my mileage.

 

Trucks VIN shows it havinbg 3.73's as part of the towing package along with trans, ps, and external oil coolers. No the computer isnt programmed for the 305/40/22 tire, which is as said about 31.5'' tall. Factory is 255/70/16 which is 30.1" tall? So I dont think that it would make that much difference. Also the speedo reads accurately with my GPS up to 40mph then it reads 45mph GPS speed shows 48mph.

No I don't have a tune yet. I am leaning towards Black Bear to tune my ecm. I dont believe that it should need a tune (on stock 255/70/16 rollers to achieve 16mpg as rated).

Tonite I picked up some used 02' yukon wheels that are 265/70/16 which are 31.6'' tall. The tires have about 40% tread left, but hey at $150 it was a good buy. Im going to install them tomorrow after work, fill my truck back up and ride them till sunday and see what my mileage is then.

Also, my truck uses a clutch driven fan, not e-fans like I'd like it to use. Is there a difference in the city mpg the newer nbs truck with e-fans have? Like would my truck equipped with e-fans acheive more mpg or is it not enough to make a difference? I've been told to cut out the front of the airbox, and replace the factory flex tube with piece of tubing. Will that help any or is it not worth doing? I have already removed the coolant hose from the bottom of the tb seeing as I live in Louisiana we barely have cold days. Even in winter we may see some 60degree days.

Any help or tips would be appreciated. Yes I know pedal effort plays a roll in achieving best mpg. But when I accel my rpms never pass 2000 till I get to cruising speed and usually I set the CC too. Only time I get on it is to pass a car or when merging onto the interstate.

 

how fast do you normally drive? any hills? And what speed does your GPS say your going when your cruising on the interstate?
A custom tune goes a long way.

I was getting about 15 all day long driving about 80mph every where with my 20s. slow'd it down to 70 and bumped it up to 18.

 

honestly every truck is different...everyones city driving everyones highway driving is different. I have found the quality of the tire and tread design as well as road surface, weather conditions and driving habits make substantial differences in mpg. all of your mods dont really mean much, in fact non factory spec'd plugs and your dual exhaust could be hurting you. I would say spend 20 bucks at lowes and make a tube for your intake since you already have the k and n drop in. With that and tune you should get a couple mpg. Honestly i have a tune, a cold air, and efans and i think all of the netted me about 2.5 mpg on the highway, and then i got rims so i get about 16-17, my denali is rated at 15.

Modern Muscle...send your truck to gm for testing..i declare it the next wonder of the world...haha congrats on the numbers. Im jealous for sure.

 

There are alot of factors that tie into mileage, it will be interesting to see the gains you get with smaller rims.
My truck would get 15-16mpg city stock, and now that its lost weight, i have an intake exhaust, bed cover, wheels that weigh less than stock, I have seen 18mpg from my last two tanks, 80%city, and when im on the freeway its stop and go.
Also there are no hills where i live, so that helps