hello i have a 2002 extened cab duelly with a steel flatbed cummins/5speed auto geered 3.55 with steight exhust. i aveage 12.5 mph. does this seem low also i've changed all the filters

 

soory i ment 4speed auto

 

Well, that flatbed sure isnt a lightweight. Now is that 12.5 in town, mixed, or mainly highway?

 

if you throw a k@N in there that will add a few more miles to your average and a cold air intake will also increase the gas mileage.

 

i drive 12.5 mph to work ,i can go the interstate at 70mph or the highway at 55mph the feul milage stays close to 12.5 . i've had this truck around 6 months. the best aveage i got was 14.5. i unhooked the to clean the termanels it went to 12.5 for the past 6 to 7 weeks. plus the truck seems way under powered. i'm thinking a programing change plus gear change around 3.90-4.11. i pull boats around 10000-15000lp range sometimes. i plan on pluing a 13500lp boat to lake fontana next summer, in which i have to go old fort mtn which is a very steep grade any ideas or sugestions will be gladed recieved

 

I could see 12.5 towing, but not unloaded. Cleaning terminals wont help. You can try a programmer; Im over 500hp and got 20 on a roadtrip this summer; staying out of it of course.

Dont use an oiled gauze filter (like K&N) Ive seen turbos that are apparently damaged because the oil from the filter gets into them. I dont have any pics handy though. Go with a dry element filter...

 

fuel filter need replacing? maybe the previouss owner ran bio for a little while