2000 4.0 misfire

Ive got a 2000 4.0, which has a misfire, on cyl 5. lets see ive swapped the plug and injector with another cyl. Misfire still on 5. ive checked spark at the plug, good. So that elimates the ignition system, and the injector itself. Now im about to do a compression test. But heres my question....the misfire is only at idle, or steady speeds, not when you get on the gas. So if the compression was low, wouldnt it misfire all the time? Or am i thinking wrong? Does anyone else have any other ideas? thanks in advance

Ive got a 2000 4.0, which has a misfire, on cyl 5. lets see ive swapped the plug and injector with another cyl. Misfire still on 5. ive checked spark at the plug, good. So that elimates the ignition system, and the injector itself. Now im about to do a compression test. But heres my question....the misfire is only at idle, or steady speeds, not when you get on the gas. So if the compression was low, wouldnt it misfire all the time? Or am i thinking wrong? Does anyone else have any other ideas? thanks in advance

If you're certainly getting fuel and spark - that only leaves compression. My brother had a 3.1L Buick Regal that had a stripped out spark plug hole. He tried to fix it with JB Weld, but that didn't work out too well. The cylinder leaked and it couldn't get any compression. It would rattle your brains at idle and would get better as the engine RPMs increase. This is just because everything is happening so quickly that the miss isn't as aggressive.

Definately compression check.

Pete