We purchased a used 2004 GMC 2500 HD Duramax a few months ago. We are primarily using it to tow a 2006 Wildcat 28RK 5th wheel. It pulls it very good, however since we have had the truck, our mileage seems to get worse and worse, whether we are towing or not.

When we first got it, our mileage seemed to average 17 - 19 mpg not towing. We just took out the new fifth and we got at the most 13 mpg. But now we are back, and we are still only getting 14 or 15 mpg. We have been filling it with Shell Diesel.

It just seems like we should be getting better mileage. DH is a very smooth driver and we generally get pretty good mileage with any vehicle, but this truly seems like it should be doing better.

Suggestions????

:help:


Portia
(Edited because I forgot to sign my name -- duh)

Check the fuel filter, oil for fuel, you could just have a dirty fuel filter, or bad injectors. The dirty fuel filter only takes 15 minutes too correct, but bad injectors can take upto a month at the dealer.

Mileage shouldn't go down after towing, if anything it should get better. In fact, the mileage should continue improving until you have 20,000-25,000 miles. The filter needs changed about every 10,000-20,000 depending on the cleanliness of the diesel you are using. I buy all mine at Flying-J truck stop, and always change the fuel filter at 20,000 miles. (I have a secondary fuel filter that I change every 10,000 miles!) I have heard of some going 30,000 or more, but I wouldn't.