Is it weird that my HDD shows up in the BIOS as 800GB when it's 3TB? It's got either 512k sectors saying they're 4K, or 4K sectors lying that they're 512 not sure which, in case that has anything to do with it.
Not really. Your BIOS probably does not support GPT so it can't recognize the large drive. BTW, the drive will have 4k sectors and the bios/OS is seeing them as 512k. Sucks a bit. Depending on your drive there might be a jumper which lets it pretend to be a 2TB drive, but older systems can't see disks with > 2.2TB.