Had a similar problem. Tried all the things you did. Turned out to be a problem with the opto board.

I ran into a similar issue serveral years ago. Ended up replacing the drac motor, resoldered all the PCB pins on the drac opto board and drack was zoomy and the game tested fine.

This past week, the game was throwing bad drac postion 1 and 3 switch. I checked all the optos and they did function. I checked the blade on the drac trac and it was alligned just fine. The drac motor functions inconsistently. Sometimes it barely has enough juice to move out of its current position even though you hear the motor humming. During Drac Test, he won't even move at medium speed setting even though the motor is humming. During Test Automatic Fast mode, he moves around fine but will still get 'stuck' at 3 or sometimes 1.

Latest Debugging:

I installed a new Drac Motor Board, converted the drac track opto harness 9-pin plug to Trifucon connectors/plug. Game rebooted and test was clean.
However, the results did not change in regard to same inconsistent drac behavior and speed. Sometimes he does not even come out of his coffin when the mode is activated during gameplay. Sometimes he gets to position 2 and stays there and won't go back in when the mode is over. Opto-10 board LM logic chip related?

I reseated the Opto-10 board connectors. No improvement. I have a rebuilt IJ Opto board where I socketed and mounted new LM chips but the board is not wide enough to mount the metal brackets for a perpendicular mount under the playfield.

I will order a new Opto board and see if that helps solve the drac issue. Thanks for the tip, SJJ. I will report back with the results.