Towing with Diesel truck

Has anyone towed a TM with a diesel truck? What is your fuel mileage? Under what conditions (speed, level highway, hills, mountains, what model truck and TM do you have) did you obtain those fuel mileage figures? I'm thinking about selling my 98 toyota tacoma and buying a used Ford or Dodge diesel. I can't seem to find any reliable mileage fugures for the diesels. Friend of mine has a 92 Dodge. He claims 22-24 mpg in everyday driving, and 16 when pulling his 36 ft. 10,000lb Coachman. Any figures you may have will help. Thanks, Grampa