It’s gonna be one expensive mess up. I would change the oil for GM-approved Dex VI. But in the grand scheme of things, if the shifts are “fine” with no lag or roughness and there isn’t TCC shudder, the ZF LG8 would have been OK. Most AT specifications are based off Dex-III or VI specs, not sure about ZF but the Japanese OEMs add aniline point and friction stability testing as well.