Not sure how you want to get to I-80. After you do ,you can stay 0n 80 until Rock Springs, WY. Take US 191 north into Grand Tetons and Yellowstone. Very scenic and an easy drive. Leave Yellowstone via US 89 until I-90. Take 90 into the Badlands. From there you can go south to Fort Robinson and across the Sand Hills of Nebraska. Work your back to I-80 and home. With your limited time this gives you a lot of interstate driving, so you can make good time. Many thing to see along the way. You'll have to decide what you have time for. Nebraska 2 is a good road and will take you to Grand Island and I-80. Hard to avoid some mountain driving , but this way is an easy drive. Have a great trip.
