I finally had a block of time to work on this, so I thought I'd report back what I found:
1. I tapped on the catalytic converter with a screwdriver and it rang out very clear - no rattle.
2. I borrowed a fuel pressure test kit from Auto Zone and tested pressure multiple ways, following the instructions Mike134 provided above and using the instructions in my Haynes manual. Here's what I found:
-- After turning the ignition on and off several times, fuel pressure eventually rose to 34 psi and stayed steady, even after I turned the ignition and let the Jeep sit for at least 3 minutes. According to Haynes, this suggests that the fuel pressure check valve and the regulator are operating normally, but the pressure was a little higher than normal, so I proceeded.
-- I then checked the vacuum line attached to the fuel pressure regulator and noticed that it looked very cracked and brittle. As directed by Haynes, I removed it while the engine was running and the fuel pressure rose to about 40 psi. When I reattached the vacuum line, the pressure dropped back to 34ish, but the connection was not very airtight because of the condition of the rubber boot on the line, so I decided that I needed to replace the vacuum line before I continued testing.
3. I bought a length of tube from AutoZone and tried to replace the entire vacuum line, but the connection was not right on the back end, so I just replaced the boot the connects to the regulator with some of the tube I bought.
After completing this setup, I retested, with some strange results:
-- With the vacuum line attached, the pressure was a little under 30 psi.
-- With the vacuum line detached, the pressure did not change and remained at 30 psi. I plugged the end of the vacuum line with my finger and heard the engine change, as it had before, but the pressure never changed.
So...based on my Haynes manual, it looks like I may need to check the fuel filter next. I already bought one, so I am headed out to my driveway right now to try to replace it. Wish me luck! And feel free to comment if you have any other suggestions.