I've got a 2000 XLT with a 5.4 and a LS rear end. At about 20,000 miles I noticed a noise coming from the rear end whenever I turned (I currently have approx. 22,000). I know it's the clutch packs slipping on one another. I've added the LS additive and made sure there was enough diff fluid, but the noise is still there. It's especially bad when I'm at a stop and I go to turn. I feel the rear diff sorta shimmy and then start hearing the clutch packs slip. Also, it only happens after everything is warmed up. This is extremely frustrating since it's mainly highway miles on this truck and the diff is supposed to be good for life. I'd appreciate anyone letting me know if they have had the same poblem and if they've been able to fix it.