340 Chugging instead of Reving

Is it possible it's firing when the valves are off the seat.
as in valves not closing totally.
Yes that is possible. I am planning g a leakdown when I can coordinate the equipment with a buddy. I did verify lift of each valve and cam lob with a dial indicator. Once peak lift was reached, I walked the valve back down.to zero while looking for a sticky spot on the indicator which may indicate the valve was sticking. None were found during that test.