another possible sollution
what you may be experiencing might not be a lack of oxygen or a draft at all, if this unit uses barber pole burners, look above the burner, there should be a metal plate that the burner heats, i've had instances where that metal plate is warped or cracked, maybe debris is falling down into the pilot or burner. if the pilot and burner flame lift completely off before going out, it would sound exactly like a few calls of mine. i had sworn several times that it was gas volume or make up air problems, but this has been the case for me several times. aslo as apposed to focusing on gas pressure, take a look at the gas volume as well. although as little of an amount of gas is used in a steam table of this kind, i would assume they would be having trouble with the bigger appliances on the line before they would have trouble with the steam table. hope that this has given you some sort of help.