I think what you may be seeing the ECU detecting a misfire on cylinder 3/4 and shutting down fuel to those cylinders, leaving you with a 4 cylinder 6 cylinder.

Try this easy test. Swap the cylinder 3/4 coil with one of the other ones. Clear all the codes. Start the car and see what happens. Check codes.

If a coil is bad you will get a misfire code for the cylinders now served by the bad coil. Cylinder 3/4 should be OK, so code 23 should not reappear.

If you still get code 23, then it's time to chase cylinder specific causes. Off the top, I would probably get new plug wires, then look into the engine wiring harness.

Have you checked the part number on your OVP? Early OVPs were bad and were replaced with a new part number. You should be able to find the old & new part numbers using search on the site.

Where's Arthur Dalton when you need him!