Engine troubles (carb)

[Mendo70C20]

I have a 70' K20 with a Blueprint 383 stroker and Holley 750 carb. Truck was running fine, and then recently, i can't keep it running. I pump the gas pedal twice, crank it over and she fires right up, i then keep the RPM's at 1500 or 2000 to let it warm up. If i let the RPMs drop below 1500 she'll start to stall out and i can't catch it, or stop it by giving more throttle. Then once she's stalled, she won't start again. Just cranks. I've tried keeping it floored, pumping the gas, you name it, won't start back up. First thought was a plugged needle thing thats below the float bowl adjustment screw, so i pulled that, blew it out and reinstalled. No luck. Then i thought maybe a vacuum leak, so i checked all my vacuum hoses, and they all look good. If the truck would stay running i'd try spraying starter fluid around the base of the carb or near vacuum lines to double confirm no leaks, but i can't keep her running. Fuel filter is full of fuel. Both sight windows for the front and rear float bowls have fuel. I'm kinda baffled. Thoughts?