Are you seeing the P0120 code at all? If my memory serves me, this is the code for 'low coolant temp'. I fixed this on my LS by installing a warmer thermostat. Turned out the beck arnley t-stat that was marked '189' only got up to around 180-189, and this threw the P0120 until I put in a t-stat marked '195' that was a napa brand thermostat, code went away. I think the ECM wants to see temps in the 190+F range, so you are very close. Does your guage tend to wander around 190-195F, or does it hover in the 180-190 range? If you see readings below 190 consistently I know this will throw the code and the MIL light. Seems like splitting hairs but apparently the ECM is picky. This is a cheap fix, so im throwing it out there, just in case that's your culprit. Keep us posted.