humphrey

I have a Maxima that runs hot after about 20-30 minutes of driving. I have replaced the master air flow, the water pump, the thermostat (faulty?), the radiator and an air sensor or two. The car runs hot and then comes back down to earth whether I have the AC on or not. It is very random and does not necessarily happen every day especially if it is 85 degrees or cooler. If I put the AC on first thing, it seems to help. Odd. Any ideas? Is there another sensor I should look at? You think the thermostat is faulty? Faulty water pump?

Thanks!