1993 Rodeo Overheating

When driving, the heater doesn't blow warm air until the temperature guage almost peaks and then all of a sudden, hot air and the guage suddenly drops to normal. This leads me to believe I have a sticky thermostat or one rated at the wrong temperature. I've read on this site all of the recommendatons to get an OEM thermostat and took to looking around the net and I found them ranging from 160 degrees to 190 degrees. What should the OEM one be rated?

Which engine do you have?

The 3.1L GM V6 - I *think* that was only in the 91-92 Rodeo's, but I'm not sure 100%

3.2L sohc Isuzu V6 93-97

or do you have a 4-cylinder?

Mine is the 97 3.2L V6 Sohc, it takes the 190 degree