really wierd problem with cavalier

Just recently when driving the 1998 Cavalier,when driving under light - medium load, the temp gauge will start to bounce up and down and the car will have a slight hesitation. There have been no codes sent to the computer. And now that the problem has been going on longer, it seems that when you come to a stop, the gauge will slowly drop down to the first mark on the gauge. (there are only 2 marks on the temp gauge partialy warm and the one before being in the red) Then when you start to accelerate the gauge will slowly come back up to some what normal operating temps. The gauge bouncing around is very speratic, it doesnt do it all the time, only sometimes. Any help would be awesome, the car has been to 2 mechanics and neither can figure it out.
 
Thanks Nick