This was my second activation of Sunset Mountain. The first activation was with K7ZO when we did a triple with 2 other summits to the NW. See that trip report here: Sunset Mountain 2015. This activation was a double with the unactivated Peak 7460. See the full trip report here: Peak 7460
There are a few parking spots to park at below the Sunset Mountain lookout. Usually there shouldn't be other cars there, but if there are you can go back down about a 1/4 mile to a saddle south of the summit where you will find a trail that will take you up to the summit. A high clearance rig is required to get up to the summit, but I guess you could call this a "drive-up" summit. A 4-wheeler or RZR would be quicker and there is plenty of parking for trailers at the Mores Creek summit parking area on Hwy 21.
On this activation, the lookout was unmanned (early in the season) so I setup right at the lookout. Last time we were there we setup south of the lookout to not impede on the fire lookout guys space. Note that during the summer of 2016 there is a large forest fire that is moving through the area north of Pilot Peak and Sunset mountain. This area will be closed for the remainder of the summer of 2016. Check the forest service websites for access after this time. This site does get good traffic during the winter for snowshoeing and snowmobiling. A winter activation would be fun, but start early if snowshoeing as it quite a trek up there.
AT&T and Verizon service was workable from the summit, but you may need to move around to get a good spot (with AT&T). APRS would be possible with a good antenna and some power to get to the distant digipeaters. My mobile APRS setup worked okay with 25 watts and 5/8 wave mag mount.
Thanks for the Q's!