Hi did route 66, on and off, and all town in between. Agree with the comment that it is hard to find route again when left it. But would suggest if you going to do it the same way as I, then you need to spent more than three weeks ... I took 3 months, and that was still not enough to get from one side to the other and see all in between.
Have a really good time thou, you will enjoy it all!