I recently bought a 2005 ford f150 5.4l 4x4 extended cab. About six months after purchase i was driving down the freeway when all of a sudden the gas exceleration quick working. ended up getting it towed to a firestone where they said it needed a new throttle body assembly. After working on it for 3 days they still couldn't get it to work properly. So I had it towed to a ford dealer where they put in a new throttle body assembly and then an ICM, which I believe to be the electronic brains for the car. But since then there has been a lag in the acceleration. And any time I'm looking for a quick response on the gas it lags, and then all of a sudden catches up. Does anyone know what may be causing this lag in acceleration?

 

Had a similar problem, turned out to be the fuel filter and a blown fuse for me.