I have a 2001 XJ 4x4, aw4, np231, with 103k miles. runs great, no problems ever! I also have a 3" or 4" rough country lift (I know they suck, but it gets the job done) and 31" Goodyear Wrangler MT/R's. The gears are stock 3.55's, but I have 4.10's and a Trac-loc sitting in the boxes ready to go...