On the fuel injection rail you'll find a valve with a cap on it. You can check the pressure there. It should be 31 with engine running, and stay at that level throughout normal range. If you take the vacuum line off the regulator on the fuel rail, it should go up to about 39. The gauge needs to have the correct fitting. You can buy the kit for fairly reasonable money if you don't know anyone you can borrow it from. If you're really cheap and have stuff lying around including a gauge that goes to 60 pounds or so, you can cob up your own using the fitting from an old R-12 air conditioning fill hose.
I consider a vacuum gauge one of the first things you should use when you have unidentified engine problems. It will immediately identify mechanical issues. Although it's not a final arbiter of ignition-versus-fuel injection problems, I've found that usually an ignition problem will cause the gauge to fluctuate but a bad injector will not. Here's a bit of what else you can see with a vacuum gauge:
http://autospeed.com/cms/article.html?&A=2393
For a really stubborn and intermittent problem, put your gauge on a long hose, snake it out of the engine compartment and tape it to your side-view mirror, where you can monitor it as you drive.
Your 93 has the Mopar OBDI system which means you can get your own codes with the key. Ignition key on, off, on, off, then on for good: you will then get your codes flashed by the check engine light. Each code has two digits. "12" is a common one for recent battery disconnect, and sometimes appears spontaneously, and "55" is the end of sequence code that tells you the system is reading right. All others are significant. Naxja member 5-90 has a nice list of the codes
HERE.