Refrigerator not as cold on gas

[sfedeli3]

I've been trying to troubleshoot my refrigerator for the past few
months. For some reason, when it is on A/C power, it cools just fine.
When I'm on LP gas, the unit will not cool below 50 degrees! I've
cleared rust from the burner, adjusted the flame height and seem to
get plenty of heat to the evaporator coil. I've also tried installing
some cooling fans on the condenser coils and inside the unit, but with
little or no change. Does anyone have any idea as to why there is a
disparity between using electric vs. gas? I would normally think that
gas would be far superior, but that does not seem to be the case and
I'm getting tired of warm beer.