Basic Info:
•Speed Test: ~50 Mb/s Down, ~5 Mb/s Up.
•Average torrent download speeds on computer. ~50 Kb/s.
•Average torrent download speeds on phone with same network and same torrents. ~2 MB/s.
•Happens on Tixati and Utorrent.
•Firewall disabled on PC. No Anti-virus enabled.
•Though little bearing, this happens regardless of whether or not i'm connected to a vpn
•Does not matter if I change my DNS servers to google DNS
•No proxy enabled.

Modem/Router:
•Changed port on PC to match the mobile incoming port. (No firewall enabled on PC)

Tixati:
•First Incoming Port: 12604(UPNP forwarded)
•2nd Incoming Port: 6881(UPNP forwarded)
•On occasion the status of certain torrents state "Searching DHT"
•DHT status = Running
•Connections settings are default
•No Proxy enabled
•Bandwidth Tab: http://i.imgur.com/0XvG1OJ.png
•Have followed http://support.tixati.com/Optimizing_Tixati  and http://support.tixati.com/Troubleshooting_Guide

Utorrent
•Average download speed is ~100 Kb/s. Sort of, it jumps everywhere from 10 KB/s to 150 KB/s.
•Default settings.

What I don't think it is based on my troubleshooting.
•Seeding problems. The same torrent can be downloaded at higher speeds on different device
•Router/Modem issue. See above, and this happens regardless of port used.
•Firewall/Anti-virus. None are enabled.
•VPN issue, this happens regardless of any VPN.
•Internet Connection. I can download at higher speeds on different devices and download at >6 MB/s on steam.
•Bandwidth throttle issue. There's about 1 Kb/s of upload on each torrent. They're not going above that. Also, my throttle for download is unlimited.
•Too many downloads at the same time. This problem happens with one torrent at a time.

Computer:
•Windows 8.1
•i5 4670k 4.0 GHZ
•8 GB 1866mhz RAM
•Main HD: 120 GB Samsung 840 evo SSD
•Torrent Drives: 2 x 1 TB WD Blue

Time of occurrence:
•I just reinstalled 8.1 onto my SSD a few days ago. Started to torrent again and now I'm seeing these issues.


I can't figure out why my speeds are so abysmal. Any help would be appreciated.

Looking at your problem i think these should solve the problem
1. Try to change the port no. from the main page (if not then)
2. try to download diff torrent or try downloading other well seeded torrent from other client (utorrent, vuze etc)
3. If still you are not getting speed your isp may be throttling your torrent network
  check it here http://broadband.mpi-sws.org/transparency/bttest.php  
 and do the test it will tell you

Thats all one can do for checking slow download other steps you have done before so thats it

What port should one be using?

There are some ports you should not be using. I did a post on that some time ago. Try a google search of the forum although I could not find it. A search of the net will do the same that is where I got the info to post. Don't use any port standard to torrent clients, they could be pre-banned. As likely 6881 would be if your ISP is limiting bitorrent.
Does not matter other than that, just use a 5 digit port and you will solve all possible conflicts. Also use one port for everything.

Last thing are you on ADSL and are you using both a router and a modem?