engine cutting out down track after in 3rd gear!

I see you tried vacuum advance and disconnected it. I never use vac advance on any cam that's at all above mild. I always find out what the engine likes for total advance by researching on the web to get an idea and testing on my own car. After that I find out what's the highest initial advance the engine can take where it still cranks and does not ping or rattle at throttle tip in off idle. Once you know those two numbers, tailor the advance curve to suit your needs. I.E. if it likes 20 initial and 38 total you want 18 degrees of me hanical advance. Try to get all the mechanical advance in as soon as possible like 2000 rpm. If it pings you either need better fuel or a slower curve. Now about your fuel. What is the ggallon per hour and pressure rating of the pump? I run a Clay Smith high volume/ high pressure me hanical on my 440 and it works very good. Clay Smith sold me a simple Enderle bypass check valve to use as a regulator. My pump is rated at 16 psi and 160 gov. The bypass valve is nothing but a check valve between the pump and carb. It has a spring in it that can be shimmed to what ever pressure you like or need and the bypass fuel goes into a return line to the tank. My engine makes about 500 hp and this fuel system has been 100% flawless. I think the other comment that your pump may be pushing fuel past the needle and seat may be correct. Any high volume or pressure pump needs a bypass of some sort.