It's the Security Alarm Relay!
I have a 2000 Jeep GC Ltd. One minute I would be driving down the highway and the next it would shut off for no explained reason. The gauges would start going wacko and then die. At this time all the dash warning lights would come on and stay on whenever the key was turned on. After turning the key off and waiting for several minutes I could always hear what sounded like the vents for the heating and a/c system inside the dash either opening or closing to reset themselves. After they stopped and all became quiet again I could restart the car and drive until it randomly happened again. We checked the compter chip error codes and found there weren't any codes. What I found was that it was the Alarm Relay that was shutting it down. The solution I found was to use the key in the driver side door by turning it to the left then to the right. I did that several times and was able to take it for a hard 200 mile drive without experiancing any problems. Hopefully that's all it takes. Good luck to everyone. Hope this is your solution.
Check out this link: http://en.allexperts.com/q/Car-Alarms-1513/1993-Jeep-Grand-Cherokee-2.htm
This is what I found.Not an uncommon event in this vehicle. This question comes up A LOT! The factory system may have gone bad from the sounds of it. Normally, you would insert the key in the drivers door, turn left, then right to disarm and reset it. If yours is malfunctioning, you can disable it for good by doing the following: The FACTORY ALARM DISARM WIRE IS purple/yellow |-| in the driver kick panel area, at the black plug. Once Located, splice into this wire with a simular guage wire, and put it to a solid chassis ground. This terminates the alarm functions entirely. However, at this point, this car would be exceedingly easy to steel, so I suggest you get an aftermarket alarm system to protect it from here on in.