Trying to figure out why my car runs so hot sometimes...

Its not pushing coolant into the overflow or shooting clouds of steam....but the gauge goes up to the halfway point and sometimes a needle or two past it. It used to stay right on the bottom part of the water symbol on the gauge.

It will usually stay cool when stopped, unless idling for like 15 minutes then it will start to overheat. If I drive above 45mph without the heater/blower on at least one the gauge creeps up to the center. I've noticed it tends to get real hot right when I get off the highway too. And once I've been driving for 2-3 hours it will just start to overheat unless I put the blower on 2-3 with the heater on.

I can find any leaks. I haven't put any coolant in the car in about 3 weeks (since I fixed a leak) and it is still right around full. Recently replaced thermostat 3 weeks ago. All hoses replaced in the last 2-3 months. The radiator was replaced in July. Radiator cap is about 4 months old. I have the stock radiator fan moved to the a/c fans metal shroud on a temp switch, and a secondary fan from a mazda 323 wired to a switch thats always on.

Any one have any ideas what I can do about this? I'm leaning towards the waterpump, but don't those leak out of a weep hole by the bearing once they go bad? Any help is appreciated..