Hi was hoping to get some help here. My 68 GTO convertible has its original 400 WT 4 spd and motor was rebuilt long ago only has maybe 3,000 miles on it. Recently when I drive it hard (foot to floor) it literally loses all power. I floor it and it lays wheels and revs high and fine through first, second, but as soon as I get to decent speed through third the engine almost completely cuts. Literally feels like fuel gets completely cut off. Engine doesn’t completely stall but almost. It just drops down to idle and almost stalls. Background on the car is that in past couple years I’ve had the original Rochester 4bbl rebuilt and also an HEI ignition installed. Engine had no issues after both of these procedures. It literally just appeared last week. I do suspect a vacuum leak because the hideaway headlights stopped going up on their own so thought I should mention that. Not sure if issues are related or not. Any help would be greatly appreciated.