1968 Pontiac Ventura car go's flat on top end

Engine Performance problem
1968 Pontiac Ventura V8 Two Wheel Drive Automatic

i have a 400, 40 over, with a 1406 edelbrock carb. I replaced the points dist. With an hei dist. The car has run great for the last 5 years. I drove it form las vegas to kansas city. Ran great! Now the car when it gets up to around 50 mph it just falls right out, no power! Pumping the peddel does nothing to help. Ive installed a fuel presser gauge and it is at 6 lbs. I also pulled the horn off the carb and checked the float height, its set 7 16th. I have also replaced the coil under the dist cap and checked volts and it is at 11 volts. I ckecked timing and set at 32 degrees at 3000 rpm. Can you think of anything that might cause this problem? Any help or direction of it could be would be a great help. Hope to hear from you? Thanks for your time.