I just realized that in my earlier response, I confused the Denali Park Road with the Denali Highway. Everything I said was in reference to the former, (the road inside the National Park), but you were asking about the latter, AK-8 from Cantwell to Paxson. That's 135 miles of gravel, and no, I did not take that route (which is open only in summer). I'm sure it's an extraordinary drive, but again, you should check with your rental car agency, to be very clear about their policy regarding unpaved roads. Some will allow it; many will not.