Toyota Repair: car running a little bit hotter, radiator cap, temp gauge

Question
Hello. For the last few weeks I have noticed that my car, a  1992 Toyota Corolla, is running a little bit hotter than usual. When I drive on the highways it usually would get no more than 1/3 of the way hot on the temp gauge, but lately has been running between 1/3 and just under halfway mark on temp gauge. The radiator is full and there is no leaking of anti-freeze. I also just replaced the radiator cap since the old one had a little bit of the gasket missing. I changed the water pump last year and the thermostat two years ago.Could it be that the thermostat is sticking just a little bit? The car does not get past the halfway mark and has never overheated. I just want to know what would make it run a little bit hotter than usual.I actually noticed it soon after I had my exhaust manifold and front exhaust pipe replaced, tho I assume this would have nothing to do with the problem. Thanks!

Answer
I don't know why it would run alittle warmer than before but 1/3 on the gauge is too low, the normal indication is near nthe 1/2 mark after warm up, maybe the thermostat was opening too early before or the cooling fan came on sooner, or maybe the cooling fan was staying on all the time and it's not now, the temperature reading on the gauge at half is normal.