9 1/4 rear?

I have a 9 1/4" 3.92 Grip in my Dakota R/T with 156k miles on it with no problems. Lots of towing cars all over, usually weighing in at 9500lbs.
I change the lube every 25k and double dose it with additive.
Even done smokey burn-outs on Brice Rd. with Dart on trailer.
However I NEVER shock load it.