There was something wrong with that rig then. My 03 250 7.3 has over 200,000 miles on it and I regularly tow my skid loader that weighs 7500 lbs w/ a trailer weighing 2500+ lbs. I still get 13+ mpgs. All this on original tranny.i've also towed my bronco with a healthy 7.3 PSD and it could maintain speed alright and accelerate good on flats, but no chance of accelerating on a hill. and it got about 10-11 mpg. so i guess the point i'm trying to make is diesels only get good mileage when they are empty in my experience. once you throw a good load on there all bets are off as driving style and route are going to dictate your economy more than anything else.