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If you're 3.55 R/P is bad, it should cost the same amount of $$$ to rebuild & reratio to 3.73. Do you know if R/P is bad! Be sure to check the axle shafts for gaulding or pitting (where the axle brg. rides).
I know the pinion is bad. One of the gears on the left LS pack is bent over & grinding on it. I first saw it when I replaced my axle seals. Bent it back and now it is doing it again.