I used to use Tixati on this PC about five or six years ago and recently started downloading torrents again so I updated to the most recent version---but I don't think this is a version issue.  I'm having a problem with torrents failing to download even when peers are available---bizarrely enough, I got about 4 torrents to work but have about 8 or 9 that have failed to download for days.  Some I started at the same time as the ones that were successful.  
What I've done so far:
I used the Tixati optimizing guide, noticed that I had DHT: Port unconfirmed at the bottom of the screen, and followed all necessary steps: I have the auto box checked for outgoing bandwidth, I allowed Tixati through the Windows firewall, and opened the port listed in my settings on my router (I have other ports forwarded for games so I already have a static IP address for this PC).  
After this, DHT is online most of time, but still says port unconfirmed occasionally.  
The true problem is revealed by what my peers tab shows for each torrent.  The status for every single one is 'timed out'.  So, I set about checking my port forwarding.  First I checked the port using telnet and it is open.  If I understand this right, that doesn't reflect any packet transfer, though.  I downloaded NirSoft's CurrPort application and there definitely is some connectivity issue somewhere, because the state for the main Tixati service is Listening, not Established, and when Tixati tries to connect to peers, the additional process threads that appear have a SYN_SENT state in CurrPorts and then the process threads die.  Apparently that means that the packets are being sent to the server but are never acknowledged---the equivalent of a time out.  I tried briefly turning off Windows Firewall and that did nothing.  I also checked to see if the router was assigning the same IP address to a different machine, but that all looked in order.  I tried changing the port type in the router port forwarding from Both to TCP and found no difference.
I've reached the limit of my knowledge on the subject, can anyone assist?

I'm replying to my own post to add information.  I had another torrent complete last night and when I looked at the peers tab, there was one difference between the peer connection that went through and the others that did not: it was from the Netherlands.  All the rest that have been timing out are from the U.S.  I'm sure that is significant but I don't know what it means . . . could it be my ISP?