I have looked through this forum and have not found any help so I am starting new thread. I am towing a 5000 lbs camper with my 2004 5.7. For the first 12 to 15 trips, I got 10 - 12 MPG with all kinds of power to cruise at 70 MPH or more. The problem is about 4 months ago the mileage dropped to 5-6 MPG. There are no engine codes showing, I have done a tune up plus,wires and air cleaner, I also had the trans serviced and fuel system cleaned, replaced the cats and new straight through muffler. None of this was done any good. I have also checked fuel pressure and the compression both are good. I have run out of things to try.
Does anyone have any ideas?
Does anyone have any ideas?