you can run 33x12.50's on 8" wide wheel, you just can't do it with your 5.5" of backspacing. tire will rub the rear spring perch.
you'll need new wheels with 3.75-4" of backspacing. 15x8 will be fine with 12.5" wide tires. or 1.25" Spidertrax wheel spacers, but most tire places will not touch a vehicle with spacers for liability reasons.