Welcome
Welcome Ken,
I have the same truck and get around 15 in town and 18 to 20 on the highway and the only thing I have done to change to a 4" pipe from the turbo back.
Mike
Do you have the new Toqueshift (sp) trans? If so I would check the pan for metal. Ford had a service bullentin out about it and a pin walking out. Mine started off with a little bucking while I was out of town with no load then two weeks later the tranny was shot.