GE Oven ZET1PL1SS Overheating only when started in BAKE mode.

Problem:

Overheats and fluctuates in ~385 to 435F range ONLY when STARTING oven in BAKE mode @350

Works good when started in other Convection Modes (set 350 = actual ~350) or OK if changed to BAKE mode 350 without shutting oven off (set 350 => actual 355-360F) after starting (preheating in Convection mode).

But if oven shut off and restarted after fully up to temp in BAKE mode @ 350 it again overheats and fluctuates in ~385 to 435F range.

No error codes. All elements and temp sensor ohms OK with minor exception, inner Broil measures 23.8 ohms vs 21.34 spec +/- 10% but it heats OK. Relays all at proper power when running in each of the 9 Test modes. All fans working but cooling fan runs on high in step #3 & #5 when broil and convection elements on but when cooling fan not specified. Cooling fan also runs at proper speed when specified in test steps #7 & #9

Temp sensor replaced WB21X22134, Temp encoder replaced WB27T10820, and main logic board replaced WB27T10819 with no change to problem.

Got any ideas what might be going on or what to do next?