1. Were you having any symptoms or was your cooling system working properly when you changed the thermostat?
2. You mean 192 degree stat, correct? What is the brand?
3. If you weren't having symptoms before you changed the thermostat, you likely have a bad thermostat right out of the box. It happens; there are plenty of inferior thermostat manufacturers. Can you get a hold of a genuine Mopar 195 degree thermostat?
Also, did you try "burping" the cooling system? Did you drain the radiator when you changed the thermostat. It is possible that you may have air trapped in the cooling system after the repair. Quite common on the 87-90. SEARCH and you'll find the best way to burp the system.
What year/engine do you have? Always best to post that in every thread you start, as there are significant differences throughout the years.