I have a 2011 3500 diesel getting only 10-12 mpg towing 8000 lb fifth wheel. Is this average for this year??I have heard of some type of plug in programmer to improve mpg. is this true? other ways to improve mpg??

 

Sorry Sunshine, but that is a pretty hefty trailer to be towing. And many fifth wheels (yours perhaps) are REALLY high, creating enormous wind resistance.
Finally, you haven't mentioned the speed you were towing. Drop it down to 50mph (yeah, pretty boring!) and your mileage will undoubtedly improve.

 

10-12 sounds about right for the weight. And like 706 said, dropping your speed a little will help a lot.

 

Sorry have to agree but with the newer engine and emission package the fuel economy is not even close to what it was. A good friend had a 1993ish 3500 single rear wheel that got 20+ MPG loaded with tools towing 3 horses in his trailer 70 MPH.