Yeah, that’s this movie.
From IMDB :
Race the Devil 1975 Two couples vacationing together in an R.V. from Texas to Colorado are terrorized after they witness a murder during a Satanic ritual.
Now I get that you can’t help but stumble upon a satanic cult preforming a rite from time to time…but it sure does seem like they flaunt it. They keep mentioning it to the wrong people and as we see, this cult reaches far and wide. You get a real sense that they’ve traveled hundreds of miles and are still running into cult members who are all on the lookout for them, not to mention the ones who are pursuing them.
The movie is tense and keeps up the dread. There’s a constant sinking feeling when town after town, cop after cop, they’re all involved with the cult. it’s well acted – this is Peter Fonda after all. It’s also got Loretta Swit in a pre- M.A.S.H. role. It’s really a good film, but suffers from writing these people as dopes – you’ve been chased across the southwest U.S. by crazy cultists and yet you’re still concerned about how dry the martinis you’re going to drink tonight are…. (maybe you ought to stay sober just in case a group of Satanists suddenly surround your camper with torches burning? But hey, that’s just my opinion)
The film ends abruptly, but I think we can guess what happened after the credits role. Definitely a good movie and available on DVD, but might be hard to find outside Amazon.