I55 is not that bad, but when you hit I294 around Chiago, you will need a roll of quarters for the toll booth (It seems like there is one every five miles). Also, I294 is the ABSOLUTE WORST streach of concrete highway I have ever been on. It is nothing but horriable washboard the entire length. Once you get to Waukegan, the road is much better and 41 is an easy drive right into Oshkosh.
BTW, that streach of I294 is even bad when compared to PA roads, which for many years have been rated consistantly as the worst roads in the US.
Have fun on your trip.
-Rich