I completely understand your situation. Having a limited time frame and trying to take in as much as you can. I have a saying, Alaska is not just a destination, it's a state of mind. Meaning you should make realistic expectations for your trip.
IMHO the Kenai Peninsula alone deserves 7 days for a first time visitor. This will give you time to enjoy yourself and not spend so much time driving. We live here in Seward and could help you with some local knowledge, if needed.
Denali is great but it's a long drive and truthfully gets mixed reviews. The natural beauty is there but seeing Bears, Wolves, Moose, Caribou, etc. is all a gamble because it's not a zoo. I have learned you need to be in the right place at the right time so see wildlife. Sometimes you will see more moose in Anchorage than Denali.
Enjoy the trip.