35 mph WOT power loss

Doc sounds like your secondary flap is opening to early there is a spring adjustment on the side of the carb by adjusting the spring clockwise 1/4 turn at a time I think you cannot go more than 1 turn max it will delay the transition from 2 to 4 . Note keep pressure on that locking screw otherwise spring will unwind . In the manual it will show you factory setup in case you screw it up.Dismiss this 408 swinger put a vid up to show how to adjust it. Doc run a man/valve body ! that way shift it at what rpm you like .