Chappy not getting enough fuel! Help!

This is my first post and I appreciate, in advance, all the help!

So I have a 77 Chappy LB80. The complaint is that it will cut out intermittently at idle, when taking off in drive (at any degree of throttle), or will cut out at speed when using full throttle. If I am lucky it will only bog and then accelerate (this is when I am already at speed) when using full throttle.

So far I have rebuilt the carburetor (gaskets, float needle, float adjustment, and cleaning), replaced the valve and filter gaskets in the petcock, cleaned the fuel lines petcock and gas tank (several times due to fuel contamination), and replaced the vacuum line going from the petcock to the carb.

I seem to have fuel going to the carb, the jets seem to be clean and I seem to be getting vacuum.

This is a relic from my childhood and I would really like to see it running reliably.

Thanks again!

Kevin