408 breaking up

Turn the fuel pressure to 7.5-8 and see what happens. If it's not blowing by the needle and seat, run it. Run as much fuel pressure as the carb can stand.

Make sure the floats are set correctly.

If you have the clear sight plugs, set the level near the top of the window and go run it. It will probably blubber a bit down low. If it craps out again, it's likely not a fuel delivery issue.