I've owned my K1500 since summer of '97. Somewhere over 310,000 miles (the odometer has needed repair twice.)
The trans failed in '99, I think, and again about a year ago. Same shop rebuilt it both times.
Both times, the planetaries were totally wiped-out. Broken teeth, bad roller bearings on the planet gears. The 2--4 band shed most of the friction material this time, that was probably the "last straw" but the planetaries would have exploded pretty soon even if the band had been OK.
The story I get is that I spend too much time in OD with the converter unlocked, which somehow disables the lube to the geartrain. In other words, I drive too fast. Not sure I'm buying that story--but they're the experts, not me.
Point is, I don't care about hardened shafts, but I could be interested in 5-planet gear assemblies. The shop that did my overhaul doesn't seem to use them, they say they've had as many failures with the 5-planet assembly as with the 4-planet assembly.
And, again...my 1--2 shift is way firmer than I'd prefer; which wasn't an issue with the stock servo.