To each his own, Diplomat Don.
Heading east in our 32' Class A, I found the stretch of US-2 on the approach to and just after leaving Leavenworth to be real white-knuckle driving, with a really narrow eastbound lane with a minimal barrier alongside a fairly long drop into the river. The number of HGVs on the road was also an issue.
When I referred to "4-lane roads", I was referring only to the number of lanes and not to the fact there was a central reservation, SR 20 is a much wider road than lots of US2. There was only one short stretch still to be finished to 4-lane the last time we were through there 4 years ago.
Although no longer having an RV, we'd still take SR 20 to Eastern WA rather than US-2. Of course living at the western end of SR-20 Spur, it's a no-brainer compared to the 60-mile drag down to Everett to use US-2. Modern vehicles can handle the 5200' pass elevation well enough. Our 02 Georgetown did the climb from Winthrop to the top of the pass at about 35 mph in 4th gear (5 speed "box") running around 3500 rpm. Coolant temp never moved off mid-range.