Sedro Wooley to Newhalem is worst part for larger rigs. It is curvy and lacks shoulders. Main portion through North Cascades is good. Yes, there is good downhill at Liberty Bell Mountain.
Numerous pull offs and view points.
Make sure you have plenty of fuel. Eastbound last fuel is near Marblemount.
Much better then using I-90, shorter then I-90 and US 97 to Omak.
Next option would be to take US 2 and then return via WA20 or reverse.
Bud
USAF Retired
Pace Arrow
2003 Chev Ice Road Tracker