Gerald,
Could viscosity have anything to do with your problem?
5W30 sounds a little lightweight to me. These engines were designed around straight 30 SAE. The only multi viscosity oil I'd use is 20W50. I live in the desert, which is only marginally hotter than your "swamps."

I/I #4101
'71 GMC Jimmy 350, sm465, np205,3.73 posi.
'68 C/10 Stepside 292 (.030 over) Offy Intake, 500 CFM AFB,Clif headers, sm465, 3.73 posi.
'67 K/10 454 project.
'72 K/5 rolling frame project.