Kilroy,
Can you explain as clearly as you can what you are observing at 50 MPH? Stumbling? Engine stops running? Won't start after it stalls? Etc?
You may not have a fuel pump problem at all. It could be ignition system related, or some junk floating around in the gas tank which settles on the pipe coming out of the bottom of the tank from time to time, such as when at full throttle when more fuel is heading out of the bottom of the tank, pulling the junk to the end of that tiny pipe.
That is why I hesitate throwing parts at problems (not saying that I haven't from time to time).
Lets say that you put that Airtex fuel pump on and the pressure is way to high and blows the needle off the seat in the bowl of the carburetor and causes a flooding condition, but the problem was electrical to begin with. Now you have twice as many problems as you had before.
I'd like to hear what you have to say about what you are observing when it acts up at 50 MPH.
