Why would said gas furnace keep shutting off?
This isn't a great answer but I want to provide something in case it helps others.  

There was no issue with my flame sensor or the ignition device.  It went on just fine but was kicking off due to some other reason.

After a lot of troubleshooting it was fixed by one of three reasons:


powering off the furnace for a couple hours with thermostat disconnected.
installing new thermostat. I was due for a new thermostat and not sure what could have been wrong with the old one.  It did run out of batteries right before this but it doesn't make sense that when I left the old thermostat it worked fine with the furnace cover off.  The only thing I can think of is the old thermostat was sending incorrect signals to the furnace that caused it to need more air during usage (maybe an AC expert might be able to give a plausible reason for this).
Reseating cover with slight gap.  I have since put this fully on but left it with a slight gap the first couple of weeks.


I did nothing else to the unit and the unit was in otherwise pristine condition - only a couple years old.