Startech SATADOCK22UE dock not reading drive's full capacity 3TB

Thanks for your question. Since the enclosure has been tested to work with up to 4TB drives, and you have already explored the other options that could cause this issue (GPT, IRST driver), it sounds like this behaviour is caused by an incompatibility between that particular model of drive and the chipset used in the older SATADOCK22UE.