PKRWUD,
I've known about the evil 160 thermostat for years, now, but it was installed by my 'tuner,' Unlimited Performance Racing, at the time they did some engine work and burned a chip for my combo on their dyno.
Not knowing if the car was 'programmed' to go into closed loop at the lower temp, I didn't bother to change it for a 180.
FWIW, the temp after the 160 was the same as before (w/ stock thermo) on the stock gauge.
I was thinking radiator, myself, but wanted to hear some other opinions. I did get a couple of "votes" for bad radiator, and some that I would NOT have thought of, like bad radiator cap!
Thanks, everyone.