Seagate 3TB Only showing as 746gb

[[TC]»Elmo«]

Like I said, when you clone it Acronis is copying across the MBR which has a 2TB partition limit. From what I can work out, Acronis Migrate can't copy just partitions - you'd need one of their more expensive programs for that.

If you're feeling adventurous and your old drive is still working fine, you could try making an image of the partition from the 3TB drive using partimage or similar, saving it to the old disk then set the 3TB to GPT, restore then resize the partition image.
It's not the simplest of things to do as it involves using a Linux liveCD and partimage has a command line style GUI.