I would start with a fluid change. Maybe open it up at that time and see what's in there. We had a Suburban, while towing a travel trailer the rear end locked up going around a corner. When it let loose I swore it had snapped an axle. It didn't, had it cleaned and new fluid. No more issues.
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Hank
70 Chevelle SS396(454), M20, 3.73
My Chevelle
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