Keep in mind that Ford (parent corporation) has 3% holdback on on all sales. Or in other words, the dealer could indeed sell you the truck for invoice. Subsequent to the sale, Ford is going to reimburse the dealer 3% of the total sale. Therefore, don't feel too bad for the dealer and make sure you toss this nugget out during your negotiations.
I have a 2005 F-150 and love it. I'm a big Ford guy and we are going to probably trade my wife's Expedition in on a new Explorer in the next month or so. Oh, the joys of car shopping...