poor mileage deisel

[cut-rite]

I have a 97 gmc 1 ton dually 4 spd automatic with the 6.5 turbo and 4.10 gears . It has 45000 miles and a 2-3 yard dump body,I am only getting about 9.5 miles to the gallon (highway 25%load before plowing season) I have changed the filters and checked the obvious. Any suguestions? What shoud I be getting? thanks, brad

 

[TLS]

What size tires are you running? This seems low, however the bigger the tire, the less miles traveled and thus less mpg.

 

[John DiMartino]

Do you have low power?hwta kind of mileage did it used to get?that is a heavy truck and i dont think its all that bad if your foot's in it a lot.My Dad just sold his 94 6.5 turbo ,it was in a shortbox 2wd 94'and had 3.42's.Its best mileage was 15 on the highway,a 350 could get better#'s.

 

[plowking35]

I have that same truck, and I get around 12-14 mpg depending on the load, and I to have about 45K on it.
Go to http://www.62-65-dieselpage.com, they are a gm exclusive web site, and someone will know that answer.
Dino

 

[cut-rite]

more info- tire size stock 225-75-16 -small for 1 ton .I have only had this truck for 10,000 miles ,mileage has gotten consistently worse from about 12.5 down to present9.5 (same load and conditions). thanks,brad

 

[plowking35]

we changed to p235/85/16
It lowers rpms at highway speeds.
Dino