I'm new to this sight but need some help. I have a 450 with 7\3 that has 240000 miles on it got it from work so I knew the truck. I rig it to pull a goose neck haul a tractor 660 miles load was4500 lbs on 32 foot trailer milage was 7. Loaded a big round bailer started home truck started bucken when you let off the gas. Went to the Ford garage they said it was a cam sensor. Headed back didn't fix the problem next Ford garage said it was a PRV on the turbo they didn't have one so I went on home. Took it to the local dealer and they couldn't find nothing wrong with it on their computor. when you start the truck it has a slight miss and it smokes until it warms up then it runs fine. We checked for blow bye and it has very little. What could I do to imaprove the fuel milage?

And what could I do to stop the smoking? I've done all of the maintance. Thank you for all of your help!!!
PS:
No one checked the milage at work beacuse we didn't pay for the fuel!
J.R. Bennett