Fishtales,
If it's like my F250 TXR there is a speed pick up hole on the leading edge of the lower unit down low. It is easy to pick up some debris etc in there especially if you run over a stick or something else. If you see it is clogged take a very small drill bit and maunually screw it into the material by hand. You can then pull the drill bit out along with the obstruction. Hope this helps and good luck!