Depending on Fuel quality(varies by state/station), the fuel system can get fouled up fast, I would give sea foam a try.

Also go to autozone or something to see if there are trouble code, sometimes you can have a code but no light on the dash.

I just noticed your 4wd that could be part of it.

 

okay ill have to try some stuff thanks for the help

 

IDK what a 4wd should get in a RCSB. I'd think better than what u r gettin. While everyone could post their mileage, I only have 2 trucks as a comparison for you. My 04 Silvy (in sig) was factory rated @ 16/19. It basically gets from 16 to 17.3 (mostly city/ or mixed). I believe I got 18.x when I paid strict attn to my habits, when working @ 4am ( no traffic/ not gettin stuck on lights).
HWY is 20-21. I went to Chicago in AUG07, got 20.6 on way out, & 23.1 on way back.

It goes down some in winter (from idling it/warmup/ slippin on roads) but stays @min. 15+ mpg. Worst ever, 14.4 in winter, I forgot I started to get rid of freezin rain on windows. Left idling 1/2 hr.

I have 3.42.

Truck 2:Sis-in-law had a 1500HD 6L. I forgot the rear gear. She usu. got ~12.5mpg. She drives more HWY too. Her bad habit:rollin on/off gas. Far as I know she never got more than 13.5. No, I didn't know her rear gear.

 

Wow, ive never gotten that low except once while towing a car running it hard..

 

How low, J?
I think that other thread that knid pointed out has some good points in it. All in all, no 1 answer can totally answer it all.

IDK if OP drives on hilly terrain alot, but I'm thinkin he does since he's in PA.

I think habits, road conditions, tire size/ tread/ weight, & maintenance (in no order) are just some of main factors to MPG of any vehicle.

I'm gonna see how a hard tonneau helps next yr. I'm gonna drive out to KC to get it. If mine goes up 10%, I'll be happy. I'm still pretty happy w/ gettin 16/17 city mix, & I romp on it, ALOT!!!

 

I get 18 city, and i have a heavy foot, mentioned mods in other thread

 

Has the truck been into the dealer for serivce or tuned recently? The tire height in the PCM could have been accidentally changed. Also, it's possible the O2 sensors are going bad and/or the catalytic converters. You might want to check the MAF and spark plugs too.

 

+1 on the spark plugs. Whens the last time you changed the fuel filter?

 

haha, I have 88xxx and I havent changed my fuel filter

 

i am ext 4x4 w/3.73 and i get 19.2.... and alot plays in role that u prolly wouldnt think as far as driving ability as said is how do u take off from at dead stop red light etc... all the tires having the same pressure(should be checked once a week well i do) are the tires stock size or bigger? and as said maintance plugs, wires etc. etc. and like i said in the other post like this as what they had on the news a while back to slow ur spd 5mphs below what the sign says as so if spd limit is 70 do 65 i do this now, i take my time from a dead stop etc.etc.