mysunnshine, what year/model/vehicle is this...?
It's a 6.0L/4L80E in a 82 Jeep CJ. As an update to this, I took it out for my second out of town trip with it last week and ended up losing the PCM fan ground control while out on the trail. When I got back to the house, I swapped in the extra PCM that I brought along and all of my problems went away. I also noticed a few other slight changes with the PCM swap such as coolant temp. The coolant temp data and the dash data were always 10 degrees different from eachother. With the PCM swap, it's now within 1 degree. With that, I will also assume that the IAT would have a similar offset now. With the PCM swap, I did no other changes. Before my trip, I did recheck the resistance for the PCM grounds to the battery just to make sure I was not inducing the issue myself. So I actually had a unicorn fail because PCM's so rarely fail......
Can you drive with a voltmeter connected to battery to see what voltage does...?