What kind of tires did you get, are they new or used, what air pressures are you running??? Bigger tires will have more rolling resistance, especially true when it comes to meaty mud type tread patterns.
You need to really check to see if there are any rubbing issues going to 33x12.5 with only a 1.5" BL. Be more adviseable to add a 2" coil spring lift along with the BL. Do you have a 4cyl or 6cyl?