hell both our duramaxes only get 14 city/17-19 hwy. one is a 2500HD CCSB, the other a 3500 RCSB
the company my dad contracts to has a fleet of them. when towing they get about 8 city on average. when unloaded, they get between 10-12 depending on who's doing the driving. me thinks the trucks are all ECLB

 

well, when i went to look at computer engineering classes at MSOE, it was a 206 mile drive one way, i had just less than a full tank. drove there doing around 75-80 on cruise control the whole way there and back. trip was like 415 miles because we got a wee lost. i used half a tank. my tank is 23 gallon. so say i had started at like 21, i used like maybe 11 gallons roughly then. its around 37 mpg. to this day, i do not know how i did that. but my dad drives mostly all highway and he lets his gas go to just about before the first red line towards empty. then fills up, that tank fill will last around 330 miles because he gets to battle traffic at times... so i guess my dads 97 silverado and my 98 are okay on gas highway. but city mileage blows... however. I conducted a test 2 years ago, going to every gas station around here and getting the same equal amount of gas and recording the miles. at the time speedway gas ran the best. i just did that test again, speedway has gone off the deep end. i didnt realize i was getting engine noises and shitty idle from their poor gas. i tried BP and performance was noticed right away. i was absolutely amazed how different my truck was. then used shell, much different again. shell seems to be doing much better for me. my friend has a SVT Contour, when he fills up with shell he gets over 250 miles and thats idiot driving. same driving same amount, he will not get above 140 miles with speedway. so some other things to think about. i was absolutely amazed at how much difference companies are these days. and its sad. it really is.

 

I have an 04 CC just like what you described . . . I have bigger tires on it now, and a cam, but I get 9-11 in the city, and 16 freeway at 55-65 and 12-14 from 70-80

it's a pig either way

 

Put a huffer on it, and get a mileage tune, I bet it will pic up a little bit.

 

Those trucks need tuned, MPG's will climb. I get best milage with my 530 RWH race tune.

 

hey man i have an 01 ccsb 4x4 HD full bolt ons and the best ive ever gotten was around 15 hwy and 10-11 city. There really isnt to much to do that does affect milage in a really noticable way sure the tune and headers might get you 1 or 2 more to the gal but ull be havin to much fun with the new pick up to bennifet from the mpg gain