Sound Like A Bad Thermostat?

I have changed the antifeeze, flushed the system, replaced the water pump, fixed all the leaks. When I am driving, the temp guage always used to remain constant about a third of the way over from cool. Now, the guage goes up a little past the halfway point and then drops when the thermostat opens, goes back up, them drops. I am wondering, is it possible for the thermostat to be sticking enough for it to cause these symptoms, or do they only get stuck all the way open or all the way closed?
Thanks,
Patrick

94 GL 3.0