What year is your bike? Is it a 2003? Did you remove the fuel pump? I have checked the screen in the petcock, I even replaced it (I crushed the one that was there getting it out).Don’t know.
But I DO know the vacuum petcock doesn’t help “suck” fuel. The vac just opens a plug. It’s a safety thing. That's it.
I have been running a vacuum-less petcock on mine for 10 yrs. no issue.
Have you pulled the petcock to check the screen, checked the diaphragm with a bright light behind it?
Could also be non fuel related, corroded common electrical ground at front coil can cause the bike to cut out.
The diaphragm on the carb top? YUP! I've taken it out 2X and check it. Once in the pure darkness with a flashlight. No cracks or splits. It's still soft and pliable.
I'll check the electrical connector on the front coil, thanks! I would think If that was the problem, it would cut out in other gears too, but I'm happy to check. Thanks!