Not sure i completely follow, but if i were you my first stop would be Snoqualmie Pass. It’s a big ski area that’s pretty empty in summer with places to park a rig. Hike either direction and you get great stuff for a few days. If you go north, you can return via the low route (Goldmyer Hot Springs) and make a spectacular loop of about a week or so, ending up back at your truck.
If you’re just going to have a couple days, maybe try White Pass south and return the way you came. Another great section.
markv