I'm going to assume that you plan to pick up US131 where it intersects with I-94. We've traveled that stretch a number of times in the last five years, towing a 36' fifth wheel. IMHO it's a good road and we had no problems, with the obvious caveat that I'd avoid going through Grand Rapids at rush hour if at all possible. They've done some reconstruction over the last few years and the road bed is in pretty good shape.
I'd take US131 through GR and pick up I-96 into Muskegon. Just out of curiosity, where are you going in Muskegon? It's my hometown although we live in Florida now. We stay at the Trailways CG in Montague.