I agree man...I swapped out the thermostat thinking the same thing. Does exactly the same thing. I have checked the T-Stat with my gun and it opens right at 180. I have also checked the temp sensor and it's dead on. I have noticed that the t stat can be open with coolant temp at 180 at the t stat housing and the coolant is still only 165 in the back of the intake. That is in the garage after warm up and the intial opening of the stat. I let it warm up for 5-10 minutes this morning and drove down to cars and coffee and it still hadn't fully warmed up. that 15w40 rotella must be some good chit.
I am going to verify my oil temp is above 180. If it's not I'll change over to a 195 stat for winter to bump up the oil temp.