Bought 03 1500hd- Whats Normal

dblount · May 6, 2011

I recently bought a 2003 1500hd 4x4. It has 35" tires on it also. I am only getting between 8-9 miles a gallon around town. I was wondering if this was normal. I know these trucks don't get great gas mileage, but just wondered if the tires can make that big of a difference. Also I have a camper that I pull some. It only weights around 6000lbs. This truck really seemed to strugle to pull it. It seemed to be around 3000 rpms going 55. Which got really bad gas mileage lol. Anyways, I was just curious what you guys thought was normal. thanks.

Stevens03 · May 6, 2011

The tires are whats killing you and the fact that I'd bet the trucks not geared for those tires. Even your mileage and speedo will be off if its not been reprogrammed for those tires. Since you just bought it, you need to do some research and find out if there was a gear swap, what gears you have and find out if the trucks been reprogrammed accordingly.

The mileage your seeing could be a simple fact that your speedo and mileage are reporting wrong due to the larger tire size.

hockeypro1411 · May 6, 2011

If you're using your trip odometer/gallons 'till full at the pump method to hand calculate your mileage, keep in mind that you're actually traveling farther than your odometer says. The larger tires make less revolutions to go the same distance, so your mileage isn't AS bad as it seems. To go along with that thought, the tires are also throwing off your speedometer. When the speedo says 55, you're actually going closer to 60-62.

As for the gears, check the RPO sticker in the 'ole glovebox. GT4 is 3.73's and GT5 is 4.10's. If the truck is struggling to pull 6000 pounds (even with 35's), I'm going to guess that it's got 3.73's.

dblount · May 10, 2011

I have 3.73 gears in my truck and I have hand calculated it taking the large tire size into account. It still isn't ever better than about 9 mpg. I was thinking about purchasing some smaller tires I was thinking about something around a 285. I just didn't want to buy new tires till I had too if it wasn't going to help my mileage out any. If there is anything esle out there that could help me get up around that 13-14 mpg mark would be great lol. I might jstu be asking for to much with that truck though. Thanks.

ruggedlife · May 10, 2011

re-gear, get the power and some fuel mileage back, i just re-geared last week, havnt even been through a full tank yet (very short commute) and i'm already noticing a decent increase in milage (according to the DIC which has been reprogrammed for larger tires/gears)

Stevens03 · May 11, 2011

I second re-gearing and having the computer adjusted accordingly. 4.56's would be the best choice to get the truck back to where it was close to stock No reason you shouldn't be able to pull down 13-14mpg average.

dblount · May 11, 2011

So re-gearing it with 4.56 and keeping my 35's is going to increase mpg and also my towing power? Do you guys have any idea how much that would cost to have done?