to the OP, you have a bad ignition switch, or key cylinder.....it's not switching power off to the ignition and fuel pump, so the engine stays running... most of the time the key cylinder goes bad first.... especially in jeeps this old. mine had the same problem, replaced the key cylinder, problem solved.
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have you done any work to your alternator? If you bypass the resistive wiring on terminal #1 of your alternator plug, your jeep wont shut off either because of the back voltage. Long shot I know, but it happened to me this weekend when troubleshooting a charging problem.
It idles fine normaly, just when you shut off the ignition that it starts getting rough.
I would still check the ignition switch. I don't think it is dieseling if the guages still work when the ignition is turned off. I have seen ign switches go bad and do exactly as you describe. In a perfect world it might go bad and give you full battery voltage when the key is off and run smooth. However, I would lean towards it being bad and not giving full battery voltage. Engine's can run like crap when the computer, fuel pump etc... don't receive good power. Good luck and let us know what you find.