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This is a '93 and I'm fairly certain the cat convertor has been cut out of the equation. The header pipe comes down past the oil pan and then goes into a muffler that's somewhere mid-vehicle and then someone has routed the exhaust pipe out the side of the vehicle just behind the passenger door. I've been under the vehicle LOTS (enough that I won't go near the vehicle these days without putting on a pair of safety glasses because I'm tired of getting rust and dust in my eyes). I'm pretty sure I recall there being no Cat under there and the vehicle smells like a non-cat vehicle when running (like unburned gasses - like an old truck).
Not to sound contrary, by the way. Just saying I don't think I have a cat. Actually, I asked my buddy if I could get one put on it because I don't like the exhaust smell of the vehicle. He said he would advise against it.

Cornfed1

A coil can cause running problems without starting problems especially under load. TPS is possible sweep with lab scope to rule out if you have access to one. Fuel pressure should be easy to check if you have a gauge. I'm pretty sure they had a test port on fuel rail, my 93 did. If you are smelling raw gas you might want to look into your pressure regulator. Is there fuel coming out of the vacuum port on the regulator?

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Cornfed, THANKS for the info about the coil. My problem is most often under moderate load. It's mostly when I start to go up a long interstate incline. If I try to just gradually climb the long hill instead of pressing the accelerator and gearing it down, that's when it seems to stumble. And it only seems to give a single stumble now. (I think my vacuum leak was a parallel problem that was likely producing symptoms that were similar but were only confounding things).

And for what's this is worth, the stumble problem arose on a long trip down to Arkansas. I'd been out driving all day and had put maybe 300 miles on it that day. That's probably the most miles in one day the jeep had seen in YEARS. Anyway, I was loping down a secondary highway and it gave a SINGLE stumble on relatively flat road and I thought...."WHAT the heck was that?" It continued to do that over that weekend in Arkansas.
In my head, that jives more with a coil going bad....kind of like how I once had a battery on a motorcycle finally give up the ghost while on a long road trip.
But I am totally guessing.

Anywho, I'll get in there and inspect the coil this weekend.
As for the fuel pressure regulator, there's no fuel coming from anywhere around the vacuum port. I've actuated the throttle cable and revved it up while standing in front of the engine and I don't smell raw gas when I do that. I don't have a gauge to check the pressure, but I need to look into HOW one would go about checking the pressure. That may be my next step.

I'll check back when I have more data.
THANKS to folks for chiming in and helping out. This is the prettiest spot I found in Arkansas on that particular trip. This view was along some dirt road where all I passed on the road was two people on horseback.
This view is overlooking the Buffalo River.

Cornfed1

There should be a service port on fuel rail to check fuel pressure with a gauge. Take the vacuum line of of the fuel pressure regulator while engine is running if there is gas that comes out of the regulator where the vacuum line goes it is being sucked into the intake making air fuel mixture rich, would smell like raw fuel out the exhaust.

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Okay....I've read just about everything there is to read about bad coil symptoms and bad TPS symptoms. I considered ordering both, but my symptoms don't fit either really well. So I haven't ordered either. Didn't check fuel pressure either since my XJ doesn't seem to have any of those symptoms. It sounds MOST like a TPS in that it seems to have a "dead spot" in a certain range and that's maybe causing the slight miss / stumble / hiccup (not noticeable on the tach). I know I can test the TPS for flat spots using a volt meter. But I'm useless with volt meters (completely useless).

What I DID do was to spend about 2 hours today going through and refreshing all my grounds. I had read in a few places that corroded grounds can cause all kinds of strange gremlins. I took my time and cleaned all the ones I could find in the engine bay. I think I got them all. Some were horrible grimy with oil and dirt.
I inspected the coil. No cracks in it that I could see.

Long story longer, that needed to be done but it didn't fix my problem. I took the jeep out and test drove it for a little over 50 miles and it still stumbles a little here and there. THIS TIME I NOTICED IT A COUPLE OF TIMES AT THE BOTTOM OF LONG HILLS. It's not always when I'm climbing a long loping hill, so I can't say it's always "under load". I noticed it at the bottom of the same hill twice whilst doing 65mph / 2k RPM on the tach. It did it as the vehicle had leveled out. But like always, stomp the gas and it goes like you want it too. It pretty much only does it on the highway.
I will say, the fact that I can feel the vehicle jerk and that I "want" to suspect the tranny (I checked the fluid level today), that kind of also points to TPS according to what all I've read.

MY THOUGHTS:
I think I cured one of my problems (part of my problem) when I fixed that vacuum leak this week. It no longer will stutter in rapid succession and freak me out. So I think I had parallel problems with similar symptoms. But my single stumble is still there.
Where it's at right now it isn't really causing drivability issues. I have to test drive it 40 or 50 miles to even get a good read on how it's doing. It's unnerving and I don't like it, but it doesn't stall or backfire or idle poorly. I'm trying to decide whether I want to give this one up to Jebus or start throwing parts at it.

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One last thing.... Curiosity got the best of me. I suspected the TPS enough that I went ahead and ordered an aftermarket (non-Mopar....FLAME away) TPS for the jeep. It was all of $12 shipped off eBay. I know...I know...I've read on here that you really shouldn't go cheap when it comes to sensors. But, I'll try it and throw the old one in the glove box just in case. If it does actually remedy my gremlin (which I will be able to tell within 50 to 100 miles, I'll order a new, genuine Mopar part.

Either way, I will report back with developments and hopefully eventually an answer to this riddle.