Burner goes out

Question

The P3 has 2 burners. The right one goes on fine with the starter and stays lit as long as I don't try to turn the left one on. About as soon as I turn the left side on they both go to simmer and than sputter out. You can hear the propane gas flow slow or stop when the left side is turned on. I've cleaned the venturi tubes and burners. Same problem after cleaning as before. What could be causing this? Interestingly enough when the tank is full the problem goes away. It's only when the tank is maybe 1/2 to 3/4 full that the problem starts happening.Could it be I need a new regulator?