I'm back to using the mini-van as a testbed
I took the computer back out of my truck and set it on the front seat of the van. Got another monitor (we use the exact same one at work) and set it on the dash. The Visteon is still in the glovebox of the van and running through the stock radio via the antenna out cable. With all of that powered up, including sending the VGA signal to the monitor, reception is excellent. It's not perfect ("perfect" being what it is with no computer in the car), but it is close.
I can reassemble some more of my truck system into the van, but when I get to the amps I'm going to have to move back into the truck since I would have to remove the back seats to get the amps out.
I still can't figure out what's better about my van. I can say that there are practically no opportunities for ground loops in the van since I don't have any audio cables in there. Maybe it's like mazda8's trunklid open vs. closed condition - just a change of environment.:noidea: