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You are going to need a full 6 of your 7-8 days just for the driving tasks of your trip. While that doesn't mean that you won't have any time for sight seeing en route, it does mean that you really can't afford to just wing it. Assuming you take a half to full day at the Grand Canyon (my assumption as to why you chose the Grand Canyon State as your destination) then you have about a day's worth of time to spend at stops spread over your 6 days of driving. That's not a lot, maybe 3-4 hours a day, including time to get to the 'attraction' and back on the road. This, then, is going to be an exercise in logistics. You will need to do all your research beforehand, know where you're going to stop, how best to get there and back on the road, and how much time you can spend at each stop. At this point you should get out a good paper map and map out your most efficient route(s) to Arizona and back. Then start looking for venues that are of interest to you. The Map Wizard and Map Center tools under the Maps tab above are excellent first order resources. After you've got a basic plan, we can help tweak it a bit, but the first cut has to be yours. One other thing to be sure to build into your trip is at least a few hours, 2 or 3 times during the course of it, where you and your friend can go your separate ways. 24/7 of togetherness is going to get real old real fast.
AZBuck