It is the real channel number, not the virtual channel number, that determines what antenna is needed. KENS, virtual channel 5.1 is on real channel 39, so it is a UHF channel, not a VHF channel.
VHF-Low, real channels 2-6
VHF-High, real channels 7-13
UHF, real channels 14-51
Thanks for the additional readings. KSAT 12.1 seems to have readings similar to the other channels, so the problem might be multipath reflections and not signal strength.
Signal strength readings are relative, so I don't know the normal range for good signals with your TV.
The Diagnostics Screen for my Sony KDL22L5000 goes from 55 to 79.
Bad signal with picture freeze, SNR below 15 dB, and errors:
Good signal:
My newer Sony KDL32R400A has a much wider range of signal strength readings:
I was going to suggest a medium gain amp like the CM 3410, but you said a preamp didn't help.
If grounding the coax shield, an FM trap, and a reflector behind the dipole don't help, the only thing left would be a VHF-High antenna with more gain to replace the vhf dipole kit.