There's a lot of whistling (guitar-wise,) think the reverb is up, might be a microphonic tube, maybe the treble is boosted a bit too, on his bridge it's slightly piercing at times, could be a number of things.
Aside from that, which is not too often, I find this performance my go-to-guitar-lesson 101. Very enjoyable, with the emphasis (and mix, thankfully) on the guitar. Even during Holloman solos, etc., the camera is still on Gatton, and you can see and hear his great backup rhythm work.
"If opportunity doesn't knock, build a door." Milton Berle