I have a 2005 5.4 2wd f150. While driving the truck runs fine until when it begins to shift from 2nd to 3rd or 3rd to 4th. When it feels like it going to shift the it's like it falls into neutral. It will rev but not go. It doesn't knock or shake, it's a smooth change. But when it doens't happen and the truck runs fine when Overdrive is turned off. I think its the transmission but I'm not exactly sure on what's causing it.