I am hoping to get some help from my fellow first gen Rx7 lovers because lots of you have been working on cars for many years like myself.

I have a 1972 scout II and am very frustrated due to fuel starvation. List of what I have done: all new hard line from tank to carb, new fuel filter, new fuel pump, blew compressed air into the fuel line going into tank to make sure it wasn't plugged and to remove "sock" if it was plugged.

Hooked pressure gauge up right before the carb and when idling I am pretty solid at 6 PSI. Going down road at 30 MPH, pressure drops to around 3-4.
Go down road at >45 MPH and in about 30 seconds no pressure and truck dies.

What have I missed? I can't think of anything. I have a spare electric pump and regulator that I am going to put in this weekend if I can't come up with something that I have missed.

Please help!