My 2005 and 2006 both run significantly cooler under all conditions after I installed the 170 degree thermostat and the DC Performance upgraded computer. They tend to run about 175-180 on the gauge when going down the highway, and with the computer turning on the fan at lower engine temps, the water temp on the gauge never exceeds 190 in any type of normal driving.
The 08 does, actually cool enough to throw a code and go into limp mode. The 08 utilizes a 185* Vs the traditional 195* thermostat.