Only question I have in response is, would it be compatible with a 99 5.9L SLT PLUS?That is interesting, my gut response would be the connectors may have corrosion on them, causing the intermittent issue. Instead of unplugging them and plugging them back in, have you tried "wiggling" them to see if you get the same "fix" result?
I HIGHLY recommend buying a can of DEOXIT 100 contact cleaner (you can get it from Guitar Center), and spraying your PCM molex plugs and PCM molex ports.
Also, I still have a new PCM for my 2001 Automatic Transmission/4.7L/With A/C and California Emissions, you are more than welcome to have it, if it will work for your year and model.
You will need to take it to someone that has a DRB-III or suitable tool to program your VIN into it.