carb problem

I got a 76 chevy p/u with a 350 motor. It set up for about two weeks without crankin it at all, I drove it the other day to find that when i get to about 55 to 60 mph the truck start lose power almost completly. The motor is :confused: still tryin to go at full throttle but it's like its not getting fuel(LIKe A SERIOUS WIND DRAG) if anyone might know what it is would you let me know...

Blocked fuel filter, or a bad fuel pump, or a stuck needle and seat in the carb.