Online search of similar problems pointed to the fan kit which is behind the control panel. Pulled oven from wall and replaced the fan kit which solved the problem. A fairly easy fix.
GE Double Wall Oven Model PT956SR2SS
The first fan kit was delivered with a cracked fan housing but the folks at AppliancePartsPros.com shipped me a replacement the next day as soon as I submitted pictures of the damaged part and packing.
Great customer service; will definitely use them again if and when I need to repair other appliances.