Jim, on any 4.0L SOHC engines where cassette failure has been observed, the engine itself is only five minutes behind. If I'm not mistaken, there was a TSB on those engines of that particular vintage for an updated jackshaft chain and tensioner intended to address a rattle noise under load between 2000 to 3000 RPMs (memory thing), not that it matters much at the point you're at with it now.