Thank you all! I tried the MBR to GPT in just the Disk Management and it stayed at 800. I then did the Seagate DiscWizard V13 and let it initialize as GPT, and retrieved the full drive capacity. I appreciate the time everyone had spent to help!
I have a USB Seagate 3TB Desktop drive that I want to use as internal. USB Connection recognizes the full drive, but when connected to internal SATA, it sees 2 partitions totalling 800GB. What might I be doing wrong?