Why would you spend the money on a new motor when it may be a simple COP replacement or spark plug replacement? Do you have a CEL on and if so what are the codes? What is the mileage and maintenance history of the truck? Do you have an 04 or an 05? If its a 05 then it could be an injector which could be covered under warranty.
2004 F150 FX4 SCAB
VMP Custom Tunes - Corsa Sport Exhaust