Temp gauge moving up and down???

Hey guys, Ive got a 96 eddie bauer with the auto climate control. A couple of months ago, I replaced the thermostat. If I start my truck in the morning and let it warm up half way and then turn the heat on, it''ll stop moving until I turn it off and then it'll continue to move up. If I allow it to warm up completely, and then turn the heat on, while it is still idiling, the temp gauge will fall back down, but pop back up when you turn the heat off. But after driving for a while, the temp gauge won't move. It's not that big of a deal, but any help would be great. Thanks!

Did it start happening when you replaced the thermostat? If so try replacing it again, just because it's new doesn't mean it works right. By where i live we have Pep boys auto, i'd say 25% of the thermostats don't work right that come from there. I don't know the brand, but i know from my friends and i's experience that they suck.

I have posted the same problem. My 96 xl is doing a very similar thing.
I may know the problem but I am waiting for a repl;y from the forum.
When you replaced the T stat did you make sure the air vent was at the top ? You may have trapped air (like mine).