You will have no issues on Highway 20, there are a few steep grades so you will need to gear down. It is an amazingly beautiful drive, we do it 4-5 times a year.
Drive into the rest area/view point at Washington Pass, and walk out to the look-out.
The opening scene from "Ice Road Truckers" is filmed just east of Washington Pass before the highway was opened for the season. Don't think about that while you're driving there. We drove over last year the day after it opened and there was a 60' high cut in the Liberty Bell avalanche chute. Impressive!