Yeah I know I eneded up going to the better business bureau to get my refurbuished PCM replaced from Ford because when I bought it I asked about the warranty and they told me 90 days from time of purchase, it failed in 40 and they refused to replace it because they said my truck was "modified" well no kidding they knew that when they installed it.
I have been running a junk yard PCM that cost me $35 for over two years now....
the PCM is simple to get to, its under the passenger side plastic kick panel under the glove box, 3 screws hold the mount in place, a single 10mm botl holds the wiring harness to the PCM, you may also have to undo a ground wire to get enough slack to work on it.
Check for vacuum leaks first, it is common for the early 4.0Ls to have lower intake gaskets leak, sometimes you can get by with just tightening the lower intake bolts.
If all the vacuum hoses check out, including the one that goes to the vacuum modulator on the transmission, use the starting fluid method witht he engine running to see if the lower intake is leaking.
Again I bet your PCM is bad.

, based on what tests you have done so far and your symptoms