If you're looking for a straight shot of highway through the UP, M-28 should be good. There is a boring, empty section near Seney (called the Seney stretch) that might cure your insomnia, but otherwise it should be fine. However, if you want to see some of the sights of the UP you may want to adjust your route depending upon what you'd like to see.
Dropping down to St. Ignace would give you a look at the Mackinaw Bridge. US-2 from there to Engadine has one nice patch along the Lake Michigan beach where we like to stop and get our toes wet (the kids always wanted to feed the gulls). Past Manistique, Palms Book SP is home to the picturesque Big Spring. South of there, Fayette SP is a historic site with old buildings and artifacts from the 1800s.
On the other hand, M-28 takes you close to Tahquamenon Falls near Paradise (who wouldn't want to go to Paradise? ;) ) and the little museum at Whitefish Point. At Munising, a boat tour along the Pictured Rocks Lakeshore might be something you'd like. Plenty of small waterfalls near Munising, if you want to do a bit of walking. Some folks have recommended Bay Furnace NF CG just W of Munising (I haven't been there but it sounds nice). When you get past Ishpeming, a detour north into the Keweenaw Peninsula takes you to McLain SP (camping in view of Lake Superior), Ft. Wilkins (historic), and the lake views along M-26.
Near the western joining of these two routes, I recommend a stop at Bond Falls near Paulding, and a small detour north to Porcupine Mountains SP (the east unit has a wonderful view of Lake of the Clouds, and the west unit offers a relaxing hike along a riverbank with three small waterfalls and to the river's mouth at the big lake.
When you get to Duluth, I highly recommend the drive north along Hwy 61 to Grand Marais. This area is chock full of lake views, waterfalls, but unfortunately chock full of campers too... so you would want reservations for this area if you wish to stay in a state park or private CG. With your rig, though, you could fit in some of the (no hookups) sites at the Eckbeck NF CG between Finland and Illgen City, and in my experience this first-come CG tends to have spots available until evening.