Get the TrailBoss with 10 speed. Although I did have have a Colorado ZR2 with the 8 speed with no issues. But there are other people who had issues with 8 speed.
Autodimming mirror is a Gentex. Paid 55 dollars for it. GM sells the mirror also, about 110 dollars. Gentex has button to turn auto dimming on/off. GM has no button.