I posted this on alt.rv a few weeks ago:
"I am towing an Artic Fox 29-5 (13,500 pounds fully loaded) with a '06 Dodge
3500 Diesel,w/ DRW, 3.73 rear end, and a 6 spd manual transmission. The
mileage varies from 8mpg (temperature between 30 & 50 Degrees F), to 10 mpg
(temperature 60 to 70 Degrees F) at a speed of 60 to 65 mph. The truck is
nearly new with 9800 miles."
and got several replies: suggesting that I go slower, and wait until I get
more miles on the motor. The electronic mpg display is up to 15% off when
driving without towing. I am keeping track of the milage under different
conditions and taking it back to the dealer. It appears that the inlet air
temperature sensor might be bad, don't know.