Is there a way to check the codes without the use of a diagnostic tool on a 97 GC?

More than likely the jeep has the OBDII connector, in this case you will need a scanner to get the codes. There are places that will hook your vehicle up for free. I know that some autozones will.

To check the codes on your 97 ZJ. Turn the key ON, OFF, ON, OFF, ON - leave it ON this time. The codes will appear in the digital odometer (i.e. P????)

For sure, your local AAMCO transmission shops will do them for free, not sure about your part of town, but they advertise locally on the radio all the time here (CA), plus get you the code's message to write down.

if you post your codes here we would be able to tell you whats wrong.