Off-chance, but possibility that your ignition module is overheating. It happened on my 4.5 to my parents before it died. I am pretty sure it comes from having the points closed too much (I forget if that'd be too high or low dwell).

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Current:
2021 Charger Scat Pack Widebody "Sinabee"
2018 Durango R/T

Previous:
1972 280SE 4.5
2014 Jeep Grand Cherokee Limited "Hefe", 1992 Jeep Cherokee Laredo "Jeepy", 2006 Charger R/T "Hemi"
1999 Chrysler 300M - RIP @ 221k