With a trip of this size you have thousands of possible attractions you could visit, and now that you have those dots on the map as a guide, you can work on those "smaller" stops along the way. This is the part where you will need to research the possibilities and decide what it is that appeals to your tastes the most. You will soon discover you could spend weeks [months] exploring between any of your 'BIG places'. If you are looking for natural beauty then the National and State parks are hard to beat, with the likes of Yosemite, Death valley and Grand canyon in the CA/AZ region being among some of the finest along with southern Utah hosting Zion and Bryce canyon among others. These two are a little further north than your current itinerary follows from Vegas to Texas, but it's certainly an option for consideration along with Lake Powell and Monument valley etc etc.

This is just a small selection covering a small part of your trip, so you can see why you are going to have to do some reading and map studying. Once you have got a few 'smaller' stops sorted out and a few more dots on the map [which in all honesty I would regard regard the NP's and natural wonders as the 'BIG' stops] your route will start to take shape, then we will certainly be able to help fill in the blanks and help to 'fine tune' your plans. I would start with working on one leg at a time, for example Seattle to SF, inland [Mt Ranier, Columbia River Gorge, Crater Lake, Lassen Volcanic Park etc] or coast [Olympic NP, Oregon Sand dunes, Redwoods NP, Point Reyes etc] or a mixture of both.

You can use the RTA map centre to create routes and find attractions, it can be found under 'Members' in the green tool bar above. If you need to 'play around' with your options first you can use Google maps and use the 'drop and drag' feature by placing your cursor on the blue route line and 'bend' your route accordingly.

Keep asking questions as you need to and enjoy the planning, it's a fun part of the journey !

Hope iv posted right wasnt quite sure so clicked a load of buttons and ended up here.
[Please keep all questions in this thread with regards to this trip. If you have trouble finding it just click on your user name and select find 'Started threads' and then post reply.