1995 sebring coupe 2.5l v6 overheating

I can drive the car in cooler temps for hours, but when it heats up the temp gage goes up too high for my taste. I thought the thermostat was stuck, but have since had it replaced. My reservior is filling when this occurs and I am not really losing any water from any seep holes in the water pump or radiator but she still gets hot. IS the water pump the ONLY thing that circulates water through the engine? Sounds stupid, but I have always either heard a bearing or seen a water leak when I lose a pump.
Also I see I must remove/replace the timing belt to change the pump, has anyone done this and are there any tricks; my guide says I have to remove the cam pulley after the belt?:banghead: If anyone has dealt with these problems before please help!!!