I was going to say fuel but you already said its not ! another cause could be valve float, I don"t see it much any more but it can have the same symptoms! Loss of power at rpm, pinging & will pick up a little more speed after lifters settle down if throttle is applied lightly! 392 Hemis & other chryslers valve geometry is very easy to throw out of wack if you dont know Chrysler!! (Its not like a chevy, EASY!) LOL
Jester