There is a clue there. Does it over heat when you gun it down a hill or on flat ground?

That sounds like trapped air to me. Take the cap off and if you can park the truck with the top of the radiator higher than the dash(i.e facing up a hill) and start the engine and let it warm up enough to see the water flowing sideways across the radiator. As soon as you start the engine turn your heater on full heat/ full blast and watch the radiator; add water as needed; and squeeze all 5 hoses: upper, lower, timing cover to lower part of block and both heater core hoses.

Sounds like overkill for "burping" the cooling system but you know i have never had a problem with a cooling system other than total failure, like having the HG blow or the clutch fan driven an inch in to the radiator, fun stuff like that.
I also have never had a customer come back after doing something in the cooling system(and dont ever do a heater core on a ford <img src="/forums/images/graemlins/evil.gif" alt="" /> or a shrocco <img src="/forums/images/graemlins/barf.gif" alt="" /> (or however its spelled, damn german Ford <img src="/forums/images/graemlins/notooth.gif" alt="" />). They are the absolute worst part to fix ever, and with the help of the parts house take two months to finish.