ejd

Thanks for all of the suggestions. I actually think I have the problem figured out. I put a hub-ometer on the truck last week and it seems that my odometer is off! Using the mileage from the hub-ometer I am right back where I should be. Thanks!

Fuel filter has about 5000 miles on them. This engine has 280 horse power. I have been traveling about 160 miles per day pulling 49000 pound loads. Prior to that i was running empties and lighter loads locally. I figure it is the differance in the weight of the loads but just wanted to be sure someone is not stealing fuel from me or that it could be due to engine problems. The truck runs very well with no other problems.

I have a 95 Mack CH613 that had been getting over 6.5 MPG until recently. Over the past few weeks my MPG has decreased to only 4.5 MPG. I have replaced the air filter, the engine is not smoking, and my last oil change was about 5000 miles ago. Any ideas on what could be the issue. I am open to any suggestions Thanks