I think you're going to find out why the OBDI is pretty much worthless and later replaced with OBDII (which some will say is worthless also.)
Sounds like you're still not looking at the ignition module even though they give the symptom you're talking about, and are known problems past and present. More so on Motorhomes due to lack of good Ford engineering for air flow.
Remember Ford sells the F53 chassis, then a MH company decides on how much of a grill they're going to use and any air flow dams. Thinking not a lot of thought is going into that from the marketing department.
Ignition modules are cheap and a spare should be in the tool box assuming the old one wasn't bad. Remember to use the heat paste if you do replace it.