The major issue with the 60e is it was designed for lighter vehicles. All the internals of the 700r4/4l60e are small and work fine for a light duty daily driver but when you start putting large amounts of torque or load on the parts they love to shatter. Clutches burn, shafts break, planetaries shatter, splines strip. If the 60e was strong they'd put them behind the Duramax.