Since you are looking for a TNC to do strictly KISS, your best option is a TNC designed to do JUST KISS. A TNC-X is your best option. Even though the TT4 and even the Tracker3 will do KISS well, they still have to be configured for it. There is also the risk that the TT4 or Tracker3 can reset and lose their settings. The only way to reconfigure then is with the config software and a computer. A TNC-X just works as a KISS TNC since it only has a KISS mode. Once you set the baud rate hard jumpers connect it to power and it just runs! USB and Serial interfaces. Very easy to use, very stable and an overall great choice for a mono-mode setup like Winlink.
Here is a link to the TNC-X site:
They come as a kit, but if you are looking for completed units please contact us and we can provide those for a build fee at sales@rpc-electronics We can even modify the stock case to have a standard DB9 radio port interface, instead of the stock two plug connector interface.