Best of luck to you, had much the same thing happen in my wife’s Jeep TJ. Turned out to be a warped cylinder head, but luckily parts availability for the Wrangler is slightly better than the Raider/Montero’s.

1989 Dodge Raider V6
2001 Jeep Wrangler 4.0L
2008 Toyota 4-Runner SR5 4wd