2000 sts overheating

How is your purge line?
I know you mentioned the TC and WP were serviced recently, first of all why? Second, make sure the small WP belt is fine.
How is overheating...in 3-5 minutes after startup, when you are strangled in stop and go traffic and at low speeds, under heavy acceleration and up the hills?
HG is not as common as the Internet would make you think, also N* will not mix coolant with oil, so no point looking for "mayo" in your oil.

What you say is not what I would like to hear (for your sake). Disconnect the purge line from the coolant tank end and put it into a 2l bottle. Start the car and let it idle. Do you see a nice steady (laminar) flow or a bubbly flow?
If is bubbly then the next step is a exhaust gas test for the coolant tank. There is a kit from any large parts store that goes for around ~$50. You can do more than one test though. Drive the car for a day or two (don't let it overheat or you warp the heads) and then perform the test. The negative test ends with the same bluish color of the fluid as the one you started. Maybe a slight hint of green (just a bit) is still OK. A green yellow fluid is BAD.
Just DON'T add coolant before the test (if you do the test will be negative).