6.05 should work just fine. I’m running it on my XRV and PintV. I’m betting the configuration wasn’t backed up and restored before and after the update. This post has the config files and instructions for loading them: GTV / XRV / PintV Power Kit - Accidentally Reset Configs / Motor Squeal on Engagement; How to Fix?
If you really want to downgrade the firmware, then the link you’re found is correct. Just note that you’ll probably still have to load the configs via the post I linked to above.