What could be the problem if after changing the thermostat in a 1993 Dodge Shadow 2.2 the temp gauge runs hot only a few minutes after starting and when slowing or stopped?

I have a 1993 Dodge Spirit which is one size bigger than your car. I have the exact same problem! However, I have a different answer. It might be your head gasket. This can be a $1000 job. I can have a crack in the head or a blown gasket. But to know this, one symptom is white oil. Check your oil and see if it smells like gas or something odd. And check if it is white. If it is that means there is antifreeze in your oil which means you have a leak in your head gasket. In my car, there is no anti freeze in the oil. I did change my thermostat a couple of months ago though to try and fix this. But nothing happened. I feel the thermostat was put in upside down or in the wrong order. So I am going to try and replace it again. The thermostat might also be closed shut. I HAVE A 91 PLYMOUTH SUNDANCE 2.2 (SAME TYPE CAR) WITH THE VERY SAME PROBLEM (S).REPLACED THERMOSTAT..RADIATOR..AND WATER PUMP..FLUSHED EVERYTHING(WHICH HELPED A LITTLE) BUT STILL GAUGE SEEMS TO MOVE FROM COLD TO HOT. HAVENT FIXED PROBLEM...BUT WHAT HELPED WAS TO DRILL SMALL HOLE (1/8 ") IN THE TOP RING OF THE THERMOSTAT..THIS SEEMED TO HELP RELEAVE BLOCKED AIR IN THE LINE...AND MOVE THE GAUGE TEMP FROM HOT TO 3/4.....IF YOU DO USE THIS METHOD MAKE SURE THE HOLE IS LOCATED ON THE TOP WHEN THE THERMOSTAT IS RE-INSTALLED(IF IT IS AT THE BOTTOM IT DEFEATS THE PURPOSE) ......THIS MIGHT BE A TEMP FIX FOR YOU NOW... HOPEFULLY IT HELPS (IAM STILL WORKING ON A PERM FIX FOR MINE) You have air in the cooling system.