You be better off asking this in the Alaska/Canada forum here. There is a long running thread on people heading up to Alaska in 2015. It seems a bit strange going up north to Rushmore (IMO one day there is plenty unless you are going to visit other area spots like Badlands or the caves) and then turning south to YNP.
As for speed, yes we used to push it until we got to our target area doing 500-600 miles per day. But since I've retired 300-350 is our target. I haven't been up to Alaska but the impression I get is that you better moderate your speed on the Alcan because frost heaves can make large 'bumps' in the roadway that you do not want to hit at high speed.
As for the border crossing, the impression I get is that if you have all the paperwork ready-passports and pet certificates ready-- then most of the time you get a quick passage thru the customs port. But they may randomly pick out RV's for a full search where you have to pull out all drawers, open all closet doors and get out of the RV and they will search it top to bottom. Again the other forum will have people that have been there.