Need to resize 3TB drive in GPT

Hi and welcome to the community UncleJake. The remaining space could also be available from the disk management window, you can merge the two partitions or format the second one.

How to access Disk Management in Windows XP, Vista, 7 or 8 to manage hard drives

How to partition and format a WD drive on Windows (8, 7, Vista, XP) and Mac OSX