Tried to become the highest truck in Washington State, heading up Hart's Pass (6204 Feet) eventually ending at Slate Peak about another 1000' or so higher, but got stymied by downed trees. Wasn't expecting this, and was on a golf outing so didn't come fully prepared w/chainsaw etc. Checking some of the overlanding groups to see if it's been cleared or not, might just organize a trail clearing party myself. The sign isn't kidding, the road ranges from wide alpine meadows where you could put 3-4 cars abreast to 'Oh god, I hope i keep the outside two wheels on the road, that's a looong f'ing way down.' Fortunately the white knuckle section is only about 1/2 mile long, but if you meet someone coming the other way, it's unpleasant to consider backing up for whichever is closest to the wider part.
If I can get this one done, that makes me want to tackle Rail Road Ridge in Idaho: The peak elevation of the road is 10,433 so hopefully you don't have a fear of heights! Add in Steens Mountain OR. The road reaches an elevation of 9,700 feet. A gated road (closed to the public) goes right to the top, at 9,737 feet to service an array of communications towers. Do these and I'll have the 3 highest roads in the PNW. Definitely a late summer outing depending on how long snow hangs around.
So an interesting question for the group, what's the highest elevation you've had yours to?