1997 Ford F-150 not running right

I am working on a 1997 Ford F-150 4.2. I have put on a new fuel pump, gave it a tune up and put in a new computer. I am still having trouble with it. It runs really rough. After it idles for a little while the manifolds glow cherry red. Someone mentioned it might be out of time, but it doesn't seem to be. Someone else said it sounds like it is getting to much fuel. Another person that I talked to owns one of these and has had the same problem. They replaces several sensors and the computer. Several thousand dollars later they are still having the same problem.