Aggressive and Unrealistic but not Impossible
Welcome aboard the RoadTrip America Forums!
Your driving time estimates are obviously coming from mapping software, and you have to realize the terribly unrealistic assumptions that go into making those estimates, such as you will always travel at the speed limit (you will never see any traffic or have to slow down for trucks or terrain), and you will never stop (your car will never need fuel, you will never need food, and nature will never call). Here in the real world, assuming 55 mph over the long haul and including stops will lead to a much more realistic estimate of the time involved. So about 550 miles per day, with 10 hours 'on the road' is a better rule of thumb than anything canned software is going to give you. That said, your daily legs are possible, just don't go in with the illusion that you'll make those miles in the time allotted, or have a ton of spare time for interesting stops along the way. I-40 is one of the major east-west interstates and is thus well maintained and heavily travelled. As with pretty much all roads, there is stuff to see and do along it, but only if you make the time.
AZBuck