Sorry to bring back this old thread too.
I had the same issue as liamjbenett and CinciTech, a Seagate 3Tb drive in esxi 5.1 with w2k8 instead of w2012 with -128mb reading in diskmgr
I found what - at least for me - the issue was
It was related to wrong GPT table with no MBR emulation
I found...