I want to upgrade to a diesel for towing our travel trailer. Need real world fuel economy numbers?

I am considering buying a diesel to tow our trailer. Can anyone tell me what they are getting for mileage out of 06-07 cummins (5.9 OR 6.7) Powerstroke (6.4 or 6.0) or Duramax 6.6. Would love to know what you get solo AND towing (and how much you tow) Are your numbers with or without a programmer like bullydog ... THANKS!

ok..i have a 3500 dodge dually 5.9. i get 20 mpg without and 11 with trailer..my trailer is a 40fttravel trailer and i do have the banks upgrade...my trailer is 16000 pounds

I know mine is an older truck but, its an answer. I have a 1996 Ford , 7.3 powerstroke. I was getting 15 mpg alone, 10 with a horse trailer, 7 with a 35' fifth wheel that was 10'6" high,@ 7000 lbs. I removed the catalytic conveter. muffler, added K & N air system, increased exhaust pipe size, down tube. all @ $1000. I now get 10-11 with the fifth wheel, 12.5 with the horse trailer, but I am running faster with it also. The truck alone, running 70, I am at 17 mpg, 65 gives me 18.5, 60 = 20 mpg, now I run @ 55 seeing about 22mpg. I track my fuel mileage all the time, I know these numbers.

Few things. 2003 Duramax: 23 MPG (the 03 was one of the better years, less power but less problems).
Hauls a 33' 5th wheel over the Colorado passes with no problems. Average about 13-15 MPG hauling the trailer.

AVOID the 6.0 Ford, they had TONS of problems.
Cummins is a strong motor, great value. The auto tranny can't hold a candle to the Allison in the GM.

How big is the trailer you are pulling? Something to consider is that Diesel in most parts of the country is about 20-25% more in cost that gasoline.

If you buy a diesel you better do a lot of pulling and you better plan on keeping it for a while. If you don't then you are probably better to stick with what you have.