i can't remember if i posted this message before, but its still haunting me.

in early 2000 i heard a guitar solo on the radio. all the way down the left hand side of the dial. not your typical pop-40 station.

i don't know if there were lyrics, because i found the song while it was already in progress. so it might have been an outro-solo? or the whole song might have been an instrumental. its hard to remember how long it went on for. because time kind of lost meaning. but it seemed like a few minutes. it kind of went on and on.
cant remember if it ended in a fade-out, or what. but i kind of don't think so

the closest i have since found is the outro solo for Invocation of the Continual One

but this was different. it was more precise. the notes were much more defined. more in the upper register. very good production. not a basement recording
i tried calling the station, but unfortunately nobody answered.

the feeling was more demonic, if you can believe that? i was literally becoming mesmerized. it actually kind of scared me. i could almost perceive a portal to hell opening up in front of me.
not much of an exaggeration.

the style was thrashy/early-death

again, this was almost 20 years ago. sort of a tall order, considering all of the searching i've done over the years.

What was the underlying music doing? What kinds of beats/riffs?

Your reference to Invocation of the Continual One reminded me of this, Which is also Morbid Angel, came out in 2000 and also has a lengthy solo closing it out.

https://www.youtube.com/watch?v=xX_TEDkW7ao

Mithras took Morbid Angel's complexity and overall spacey tendencies to an upper level of demented cosmic proportions; did you check them out? They had a demo in the early 2000ies, and then the debut album was released in 2002.
https://www.youtube.com/watch?v=lixivQzJb4c

Their second release in 2003, Worlds Beyond the Veil digs even further this furrow bringing the listener to other whimsical sinister dimensions; an example: https://www.youtube.com/watch?v=tmYgJPOEH2Q

Could it be something by Vader???