Help Me Diagnose My Miss

I warmed up my 340 Dart earlier this morning and started driving it down the street. It fired up like normal and was running great. A couple lights down the street, it suddenly dropped rpm and tried to die. I was able to nurse it over to the side of the road and nothing was out of place under the hood. I ended up nursing it home and it sputtered and popped the whole way.

The engine is a 340 w/ mild hydraulic flat tappet cam, 750 Holley DP. Ignition is MP electronic distributor w/ HEI module, MSD blaster SS coil, generic plug wires and RC12YC plugs gapped at .040".

It's running like it's got a mean miss. It doesn't want to idle and back fires out the exhaust when under load. The AFR gauge is reading as normal. Because I've had issues with the carb in the past, I swapped in a different carb and it ran the same. I swapped in my spare HEI and it ran the same. I checked the spark w/ a timing light and all 8 wires are receiving spark. The plugs all look the same as well. I've also checked a few other items as well. Coil seems to be receiving normal voltage.

Any ideas what I should check next? I'm assuming it's ignition, but am pretty perplexed at this point considering it happened so quickly. I appreciate your ideas!