‘71 Dart with 340 motor stalling problem

Dart keeps stalling after running for 15 or so minutes. I’ve replaced the ecu, coil, ballast resistor, fuel pump and carb. Thinking it might be vapor lock, I even put a heat sleeve on fuel line - still no good. Car runs super strong for first ten to fifteen minutes. After it’s run warm for a few minutes I can feel it begin to stumble when just cruising 30-40 mph. Pedal will cut in and out for a few miles then normally (or maybe coincidentally) when I let off gas to slow down or come to stop engine cuts out completely. Not sure what else to check at this point. Any idea what would cause a stall like this after motor runs at temp for awhile? I should also mention that the engine temp is good. I have an electric fan that keeps coolant temp around 180-185. Could it be a wiring/grounding issue that shows up when engine bay gets warm? Getting a little frustrated because it runs so good when cold. Any thought would be greatly appreciated.