“Wonder if a remote login by tech support will be able to tell if the sensitivity of the tuner is affected?”
I think that the support tech would only see lower signal levels on the 3 physical channels which you are currently receiving.
The’ tvfool’ chart which you posted predicts that the 3 channels you are receiving are 31.0dbm, 31.1dbm, and 33.4dbm. The next strongest signal is WLFT which is 40.1dbm.
These power levels are on a logarithmic scale. The difference in dbm is greater than 6db which is a factor of 4 on a linear scale. As an example, if WVLA is 1000 microvolts than WLFT is 250 microvolts.
With this much difference, you could be picking up these stronger signals off a side lobe of your antenna. (Especially with your proximity to those transmitters) Look up in your attic and make sure all of your antennas are still pointed in the correct direction.
There could still be something wrong with the coax cable running from the antenna to the Tablo. Move the Tablo to the location of one of the other tuners and use its cable. (After verifying that the other tuner can receive channels which the Tablo can not.)
If you are still only getting 3 physical channels, then it would seem that the Tablo front end has been damaged.
I have seen this sort of thing happen in an RF spectrum analyzer where it was connected to a receiving antenna. We get used to the idea that an antenna has only very weak signals but that is not true if it is close to a transmitter. (Even a WiFi router transmitter)
I see that you are discussing making antennas. Are you a ham operator?