So pull the intake and exhaust manifold, and inspect for the all too common craked exhaust manifold, which gives a nice ticking sound. If I'm wrong, you're out the cost of a gasket... if not, whatever sanity you started with may return when you replace the exhaust manifold.
97 TJ Sport - 4.0/HP D30 w ARB/8.8 w LS/4.88s; 35s and flat fenders on 2.5 lift
84 CJ7; frame off restoration in progress.
The technical advice you get from me here is worth exactly what you paid me for it. Warranty issues will be reimbursed at double what you paid me for the advice.