MC pulls onto the shoulder of a highway and pitches a tent for the night. Wakes up in an ersatz Texas with a mechanical horse, becomes a lawman, and meets an intelligent dog that's an alien. There was a sequel that may have been unfinished. About 15-20 years ago?
I believe you're looking for 'Oh hell no!'. I can't recall who the author was but if I'm remebering right he pulled it from SOL.
Oh hell no! by Terriblethom (DELETED)
The story 'Oh Hell No!' by 'Terriblethom' was not found.
It was deleted on 2013-01-16 00:53:11.
Reason for deletion: Deleted at author's request
https://finestories.com/s/10457/oh-hell-no
https://finestories.com/ablog/Terriblethom
https://storiesonline.net/d/s4/t4335/oh-hell-no
https://storiesonline.net/d/s4/t422/lost-sci-fi-story
As frustrating as it is that a once-read story is now gone, I have to respect an author who doesn't want incomplete stories available.
There are so many authors on SOL who have 2 complete stories and 10 "incomplete and inactive". If you're not going to finish your story, I'd rather not get hooked on the premise.
YMMV of course.