Car thinks is overheating....Help!!!

[diver4ever]

I changed out my Thermastat about 5 months ago when my car stating to show it was getting hot. Ofcourse I changed my thermastat and my radiador cap. The thermastat is the kind with the rubber o-ring. Hate this kind. Anyway, if I drive for sometime, the cars needle starts to go up. I run the heater, it goes down. If I drive about 2 hours the needle goes all the way up thinking the car is overheating. When I pull over to check it, it's not over heating with all the steam and everything that comes with an overheated car. I check the water and it needed none. Could it still be the Theramastat? I've never worked with a thermastat with a rubber oring. It was a very tight fit when I put it on. Any suggestions?
P.s
Just checked to see if both fans are running and they are. I can sit at an idle and be fine. Once I start moving it's go up a bit, take my foot off the gas alittle it goes down alittle. I'm at a loss here.

[ikeyballz]

pull out the T-stat, make sure its the right size, make sure its opening..and for a little while, try running the car without a tstat. if its running cooler without it, somethings wrong w. the thermostat.. if its the same thing, well.. something else is wrong?