360 running on 4 cylinders

Thanks, wow that's a lot of suggestions to respond to. I'll try to here;

1. The gas tank, it's new along with the sending unit and pump. Only the fuel line is original. We replaced the fuel filter with the Holley install.
2. Timing is good, 12 degrees initial and 32 degrees all in.
3. Spark gap check, I stuck a screwdriver in the boots and measured a good healthy spark about a quarter inch from the engine as ground. The spark plug gap is .035" I also checked to see if I had good spark with the plug grounded to the engine.
4. Compression is good cold and hot. Leakdown is ok I think, not really sure how to measure that properly other than watch the gauge after the compression test.
5. The ignition system is bone stock except the coil is a MSD Blaster. Even the distributor is stock. Popped the cap and inspected it, no issues noted.
6. Nope, no rag in the plenum. I did check while I had the carb off for the second time.