I see in the latest edition of Hemming's Muscle Machines there is a fella with a 69 Dart 383 4 speed car & 3.23 SG with the same problem that wrote in. His car is original also with the drive train rebuilt. Common theme it appears. He has also replaced the clutch twice. New flywheel and various parts as well.

1968 Barracuda Fastback 318-2BBL 904 2.76 Frost Blue Survivor
1970 Roadrunner 440+6 BBL 727 AT 4.10 SG Dana Blue Fire Metallic
1971 Cuda 340-4 BBL 4spd 3.91 SG Curious Yellow
1972 Barracuda 318-2 BBL 904 AT 3.23 1 Legger Tor Red/White Vinyl Top
2007 Dodge Ram 1500 5.7 Hemi AT Patriot Blue
2011 Dodge Challenger RT 5.7 Hemi 6spd 392 SG Triple Black
2014 Dodge Charger RT Max AWD 5.7 Hemi AT 305 Billet Silver