My GE profile gas range oven JGSP48B0H3BB will preheat but once the set temperature is reached, the igniter and gas turn off and never cycle back on. So, the actual temperature steadily drops over time resulting in food not cooked properly. Example as follows:
Turn Oven on set bake temp to 375
Igniter glows red, flames light
Actual temp increases until it reaches set temp of 375, beeper sounds.
Igniter turns off, flames go out.
After 10 minutes, the actual temp has dropped to 325. Igniter comes on but flames do NOT light***
*** If I open and close oven door, the flame will relight almost instantly. The oven will heat to set temp but then the temp will steadily drop again.

What I have done so far:
Replaced igniter.
Replaced Temperature sensor.
Measured 3.25 - 3.28A current flow through igniter wire using clamp on ammeter (when igniter lit).
Replaced Control Board.

Other observations:

- Initial ignition occurs but seems to take longer that expected (i.e. 3-4 minutes).
-Preheat time is normal

Any Ideas? I'm reluctant to change the safety valve since it works during initial ignition and when oven door open/close but I'm at a loss here. Could this be related to the door switch?