Goodman / GMC 125-5 gas furnace in an unconditioned crawl space with concrete floor surrounded by dirt. When the outside temp gets 40 degrees or less in Atlanta, GA, the heat stops. When I immediately try to restart it, the igniter glows orange for 7-8 seconds, but no gas flows. We can turn off the thermostat wait 15-30 min and it fires back up. Sometimes it?ll work for only 15 mins. Sometimes it?ll work until it gets cold again a few weeks later. Could the outside temperature affect gas flow? or Does the furnace working overtime because of the low temps cause something to overheat? loosen? And shut the whole system down? What could explain the waiting a short time then working again? Gas water heater 6 feet away has a standing pilot light that stays lit. Four techs have been out here and tried various fixes that did not work. The following parts have been replaced: thermostat, capacitor, board, gas valve, vent fan unit. Flame sensor has been sanded. Has anyone fixed the exact same problem?

The answer to your first question, yes. I would ask your gas company to change the second stage regulator. Because this is their property you should not be charged for the change. The answer to your send question is, corrosion. Check all wiring connections at the thermostat and furnace. Check all ground wires including power to the unit and at the circuit breaker box. It could be as simple as a bad door switch or bad connection at the emergency switch. I see that the pressure switch has not been changed. Check to see if the venting is free of restriction. Is there a diagnostic light on this model? The waiting makes me think a coil such as a transformer or relay issue. It cools off and re-energizes. I hope this helps. When the ignitor glows, is there 24 volts AC going to the gas valve? If so, gas issue or gas valve (I know you already replaced it). If not, bad connection on board, burnt out relay or another bad board. May I suggest finding a tech who knows the Goodman forward and backwards.

HI!
There are a couple of things I would check that may not have been checked out before.
First of all is your system natural gas or propane? If it is propane there may be a low gas pressure control that is upstream of your furnace gas valve. If your gas pressure is too low it won't let the gas thru. I live in North Dakota and I run into that once in a while on propane.
Another problem could be the gas regulator. The pressure may be set too high and it will lock up your gas valve when it tries to open. This holds true for both natural gas and LP. Or your gas regulator is sticking closed at times especially if it gets very cold outside and it has moisture in it. A new regulator is very inexpensive, about $20.00 or so.
Does your gas valve get at least 24 volts to it when its suppose to? If you have less than 22 volts to the gas valve it may not be opening consistently and even though it might open and operate it may drop out at any time. Make sure the transformer secondary side is at least 24 volts and that there are no loose connections in the gas valve circuit.
I see you said that the flame sensor has been cleaned, but did the tech also clean the grounding field for it? This is usually the end of the burner the flame sensor is located on. Also if the burner is loose in its bracket you won't get a good ground and the gas valve will drop out if it doesn't keep its micro amp circuit thru the flame.
To answer your questions, yes, cold temperatures can affect the gas flow as far as the gas regulator sticking closed, but it usually has to get below freezing. I wouldn't worry about your furnace working to hard in Atlanta, it doesn't get cold enough to run very much.
Have a qualified tech check out what I mentioned, or maybe the previous techs have, and se if I was of any help to you! Good luck!!