I think it would be worth it to find a tech with a scope. If he knows how to use it then there will be no guessing. Electrical , rich or lean misses all look very different on a scope. You can even see for sure if the Opti spark is acting up.

 

The '93 Z28 I had did that when the alternator was going out,drove me crazy for a while then it died completely and quit charging.

 

I'm definitely going to have it towed and looked at. My pops could read a scope like nobodies business, but he's busy with retirement life, and i don't blame him! 🤣 I will definitely keep this post updated with the conclusion( as long as I'm not bankrupt)!

 

Just a FYI, you can buy a scope that plugs in to a PC/laptop for cheap. Search Amazon for Hantek they are around $100 and you can get an inductive pickup used for secondary ignition for $20. In theory you could see youtube on how to hook it up then just send screen captures to your dad.
I am one of those old timers myself and I have the Hantek 8 channel with most of the accessories, I also have old school 2 channel scope from the 70's, Frist thing I did with the Hantek was check accuracy with a wave signal and it was spot on.

 

Could be the valve stem seals. I installed new ones incorrectly during an overhaul and had horrible backfire on accel and decel. The oil was basically free flowing past the valves. But this is happened a 3.4 v6