Lambchoppers gets Metallica tones several years later. EVH 5150 III is hard to dial in 80s thrash tones on the blue and red channels because it has that midrange bark that is inherent in the amp.
You hear him hitting the tones you want at the end of the video.
The easiest way to get versatility out of this amp is to use the green channel with a pedal. You will hit Metallica tones with no problem that way. Try a JCM800 type pedal in the front. I wish after years of using this amp that I had found the right distortion pedal green channel configuration. I have the 6L6 version, not the EL34 version so found it harder to get there but I got there.