US-131 is freeway all the way to the Manistee River, and then there are only at most five towns to slow down for between there and Charlevoix (Fife Lake, South Boardman, Kalkaska, Mancelona, East Jordan).
US-31 through Grand Haven is a mess at most hours due to obscene traffic (50,000 AADT) and poor design (lots of stoplights and a drawbridge). In my opinion, Grand Haven should have been bypassed 20 or more years ago. The freeway around Muskegon is quite tight, but from roughly the north BUS US-31 merge to Ludington, it's mostly smooth sailing. From Ludington to TC, it's mostly two-lane that flows right along, but watch out for the 30 mph zones in Manistee and Bear Lake. Traverse City is a mess at all hours, especially during the Cherry Festival (July 7-14).