Sci-fi: Universe as simulation. Native American elements?

Read perhaps 10-15 years ago. A man (person?) realizes the world is a computer simulation, and (I think) gains some ability to alter reality. If I'm not mixing up books, shamanism and peyote use may be tied in. I think he's opposed by mysterious/powerful others, who in one scene pursue him with guns through some sort of meta-reality. I think the overall tone may be fairly dark.

Yes, I realize--except for the Native American elements, this could almost describe the Matrix. :-) I'm sure it substantially pre-dates at least the Matrix movies.

Zelazny's Eye of cat ? Don't remember much about story specifics, but it has strong native american elements and a dark tone.

It sounded very promising, but looking at various synopses I don't think Eye of Cat is the one--I'm fairly sure I haven't read it. :-(

this is not as old as you are citing, but your description sounds so much like the novel The Traveler by John Twelve Hawks...written in 2006.

I don't think this is it, but it's been long enough that I don't remember the details (other than the most superficial "it has Native American and computer-simulation elements) , so just to rule it out, have you considered Cyber Way by Alan Dean Foster? It wouldn't have been new at the time for your time window; it came out in the early 1990s (but then, something that "substantially predates the Matrix" is already pushing 15 years, since the Matrix is 13 years old itself.)

the series including The maker of Universes has some of the aspects mentioned, but not all

My humble apologies to those that commented on Dec 20th! I dropped out after the initial round of responses, much to my loss. I can certainly see that The Traveler sounds similar, but I'm almost sure that Cyber Way is *the one*! Lorax, thank you!