You should need a new steering stabilizer for 31" tires, I run 35" MTRs and don't have any issues with them at 75 MPH. You may want to have your alignment checked, or check it yourself. You can also check all the bolts in the front end to make sure everything is tight (especially the trac bar). Other than that, I got nothing!
Good luck with the tires, I have been running them on my rig (one size or another) since I picked it up in October of '02 and have been happy with them.