98 Trans Sport gauges

I just had a new motor, 3400, installed in my 98 Trans Sport. The new motor has 16,000 miles on it. I notice the thermostat gauge does not return to 0 when the van is shut off. Even the next morning it is exactly at the same running temperature until I restart the engine when it does return to zero. It heats to the proper temperature and there is no overheating. Also the tach does not return to the pin or 0 position just to 300-400 rpm when shut off. What could have changed with the new engine? Any help would be greatly appreciated.