Norcold Refrigerator Carbon Buildup on Flame Probe

Id checked the gas pressure too. If the pressure is low, the btu input will also be low but it will also draw in less primary air. A dust free, clean orifice is also important, but that doesn’t sound like it would be a problem in your case. Be sure the burner is super clean, so nothing restricts the primary air intake.
If it still soots after all that cleaning Id figure out a way to get more primary air… by hook or by crook, there are ways. Craig