I have a 1992 318 Magnum engine swapped into a 1956 Dodge Regent. When it's cool, it will run pretty good, though it has a high idle. When it gets warm, the engine will start to misfire, drop cylinders, and make such little power that it will die when you put it in gear. I recorded what it does when it gets hot. In the second clip, I was losing speed while going downhill. I feel like it's heat related because it doesn't happen during winter, could it be the ECU getting too hot?

 

Coil or crank sensor would be my guess. Putting the pcm in the middle of the fire wall where it receives all the heat is not a good place for it.

 

I've already replaced the coil and crank sensor.

 

I'd put a timing light on the coil wire and verify it's loosing spark. That's what it sounds like.

 

I don't have a timing light, but I started pulling plug wires which showed that all of the cylinders had spark. I did find out that if I leave the hood open, it will idle just fine. But if I close the hood, it starts to misfire and idle high.