First, measure the angles of the u-joints at both ends of the rear drive shaft. The AW-4/242 combination is longer than the AX-5/231, which means a shorter drive shaft. The same amount of lift will thus cause more of an increase in the drive line angles. A SYE is always a good idea, but you might be able to eliminate the vibrations by shimming the rear axle to adjust the pinion angle, or perhaps a transfer case drop (although I really, really dislike those as a matter of principle ... but many people have found that they solve the problem).