Not sure about factory GM cranks, but this might be an option for you.
GM DURAMAX 6600 Crankshaft
Crower Crankshafts are made from the finest quality materials in the world. Our top of the line forged cranks are made from aerospace quality, vacuum degassed 4340 chromoly steel. Our 4340 forged cranks are "non-twist" drop forged for the strongest crankshafts on the market. Crower's billet cranks utilize either 4340 or EN30B materials. It's your choice at Crower, we make what you want and need for your application.