We've done that segment are will be doing it again next summer. The biggest difference is that we leave from WI instead of TX. There is so much to do out there that we've taken to splitting our trips. We'll spend 27-28 days on the road and we'll do Washington with a touch of Oregon one year and then northern CA with Oregon the next year. If you have 5-6 weeks you can do it all. If you have less time, the biggest problem is deciding what to cut out.
In the past we've gone into CA via Donner Pass and Sacramento, then heading north. This year we plan on entering CA from Reno and heading north on US-395 to Susanville to save some time and skip the heavier traffic. From there we'll head across to Eureka on the coast.
The redwoods area gets really nice, they begin just south of Eureka. We chose to base out of Eureka, then take the toad south (and north) to explore these areas. After that the drive up US-101 to Crescent City (the place that got leveled by a Tsunami during the 1964 Alaska Earthquake) is also nice and we spend a few days base camping in Crescent City.
Leaving Crescent City you have two options. You can head inland to Crater Lake or go north up the Oregon coastline. Crater Lake is best seen later in the year, July or August. They get plenty of snow up there and the loop road wasn't fully open yet the end of June last time we were there. Crater Lake is a very deep brilliant blue lake that's in the crater of an extinct volcano. After Crater Lake be sure to return to the Oregon coastline at Brookings.
The Oregon coastline is the best of all the coastlines. There are numerous sea mounts and geographical features along this area that are truly amazing. Harris Beach state park in Brookings is a great place to begin and it ends up at Cannon Beach and is filled with lots of great scenery in between. The Oregon Sand Dunes (you can rent dune buggies) are found around Florence, the Blimp Hangar and cheese factory at Tillamook, Sea Lion Caves at Florence and a zillion light houses dot the coastline - most notably Hecta Head at Florence. Lewis and Clark stayed at Astoria at Fort Clatsop as a natonal park, which is recreated and interesting if you're into history.
If you have even more time you can head east towards Portland. Just south of Portland, at McMinnville, is the Evergreen Aviation museum, which is the home of Howard Hughes' huge Spruce Goose that was supposed to ferry troops across the Atlantic in WWII. The Columbia River gorge features many waterfalls and interesting hikes, most notably Multnomah Falls.
Heading across the Columbia on I-5 you get into Washington. Mount St. Helens is a must see. There is an excellent visitor center at Johnson Ridge. Be sure to see the movie (the screen opens up at the end with a view right into the lateral blast crater). You take the road into the area from Castle Rock, on I-5. After MSH, we prefer to not take I-5 up to the Seattle area. Instead, we head over to Aberdeen and pick up the coastline starting at Queets or Kaloloch. There is a great forest service campground right on the beach just south of Kalaloch Lodge that has awesome sunsets and you can hike down the beach to stands of redwood burl and bald eagle nests.
The WA coastline isn't as awesome as Oregon but it takes you to some pretty neat places. You can take the spur into the Hoh Rain Forest portion of Olympic Nat'l Park (just south of Forks). If time permits, you can also go to the most northwesternest point in the continental US - Cape Flattery. Here you'll see some intersting cliffs andcoastline on the Makah Indian Reservation. Later on continue around Olympic Nat'l Park on US-101 past Crescent Lake and into Port Townsend. If you stay in Port Townsend I'd recommend Fort Worden State Park. It's an old coastal artillery fort where you can camp right on the beach and go explore the old gun emplacements. It's very accessible to downtown Port Townsend, which is a museum of Victorian architecture and a very interesting place. Basing out of PT, I'd be sure to tour the Hurricane Ridge and Sol Duc Falls areas of Olympic Nat'l Park. Also the Dungeness spit and Olympic Game Farm in Sequim.
Leaving Port Townsend, take the ferry across to Keystone on Whidbey Island and drive up through Deception Pass to Anacortes. Base out of Anacortes (we stay at Fidalgo Bay RV Resort) and be sure to take the Island Adventures whale watch cruise to see the Orcas frolic around in the Straits of San Juan., Then take the ferry over to San Juan Island and day trip the island and Friday Harbor. You can also take the toad down to Seattle and see Pike Place Market, the Space Needle, Underground Seattle, etc.
Anyway, these are some of the things I'd recommend seeing. I've posted a number of these photos in the IRV2 photo section, if your interested. The biggest problem is finding enough time to do it all. I hope you have a digital camera because you'll go broke buying film otherwise.
There's some great scenery up there and I'm sure you'll enjoy it. Like the knight says - "you have chosen wisely".