Alright I'll try a few of these ideas. The thermostat is brand new from Nissan, so I'm guessing its not that. I've been considering taking it to get a full system flush. I haven't found any milky coolant/oil in the coolant.

The radiator is only a few years old but I guess it could have gotten clogged somewhere.

I might try this last idea that jtmroczk had, and if that fails, go for the coolant vacuum flush.

Thanks for the input guys. If you have any more ideas let me know.