Originally Posted by SilverColeTrain

Fp was 39.88psi. So that rules out fp, bc the DM is apart of the pump sending unit I believe.

Originally Posted by 2002VertGt

That's the thing bolted above the rear axle that corrodes right? If so its already been replaced...

Originally Posted by SilverColeTrain

The cats could be clogged. At work it usually ends up being the throttle body. What it sounds like seeing you only have 5 to 10% throttle available it's in a limp home mode. I have a throttle body. Pm me for details. But one easy way to tell if its the cats is to disconnect them at the manifold and run it down the street and see if it runs any better. Do not run it for long time or you will burn a valve. My truck had the same problem 10k miles ago and I had to replace the throttle body. When I was diag the problem I still had my stock manifolds. So I detached them and put headers on and the same problem was still occurring. I ended up replacing the throttle body and changing plugs and it cured it. Do not over think this. The tp sensor and plugs are known problems. Start small then work to big. I don't think the tp sensor is available separate from the throttle body from ford. But an auto parts store will most likely have a separate one. Please keep me updated.

Originally Posted by techrep

After the truck reaches normal operating temp or when it mis-fires...pull over and look at your cats...if they are super hot or glowing...bingo