This worked for me today on my 2001. For me it was Torx T10 for those keeping score.

As far as removing the plastic cover goes, I broke mine. It is held by two tabs - a short one at the front (toward the front of the truck) and a long one at the rear. I think you are supposed to pop off the front tab, then somehow carefully pivot to allow the rear tab to release.

Not knowing that, I just pried it off and the rear tab snapped. Being 16+ years old may have made the plastic brittle. Me being way older than that may have made me not care too much about things like that. So I put a screw in it to hold up the back end. One day I'll buy a new plastic cap if that's the last thing between my truck and perfection.

T15 on mine, but they weren't loose, so my passenger mirror still is a bit :/