I like the US-63 suggestion. But I kinda like doing my 63mph in the right lane of the interstate watching almost everybody go by me. Plus there are rest stops, food & gas.
I90/I39 south has one toll at the Wisconsin/Illinois boarder. If you have EZ-PASS or I-PASS, no problem. Without a “PASS” of some kind they mail you a bill and charge you more. Then you follow the I39 signs south at Rockford. I39 to I80 & I80 east. There is a toll where I80 joins I294.
A note, from Rochester to where I80 meets I294 is over 400 miles. For me that to much for one day. I would suggest getting off of I39 at the 72 mile marker exit and take Rt 34 east to the Sandwich County Fair campgrounds for a night or more. Electric, good water & dump station. I have used it for many years to see my kids in the Chicago area. In town you can go to Johnny K’s for a real Chicago hot dog (with seeds) with everything or Italian beef sweet & wet (they reheat great). Also in town is Benda’s Frozen custard for a different type of meal. You can go east from there and pick up Rt 71 or Rt 52 south to get back onto I80 east.
NEVER take an RV through Chicago unless it is a class B. Well, unless you are a real masochist with nerves made of steel.