The auto 4x4 switch is defiantly a problem, so mush that is probably isn't a problem, because if it was weak the previous owner or warranty probably took care of it.
My dad bought a 2000 Silverado 5.3 new and the switch went out in the first year. It was a city truck so 4x4 wasn't used... still broke. Then He traded it for a 2003 Tahoe 5.3 and the same switch broke again. The Center counsel/center seat latch broke on both too. I think warranty covered it though.
I've tried the "auto 4x4" mode and its to slow to do much good. It will switch back and forth repeatedly. It detects wheel slippage then turns on 4x4. Pulls out as soon as the wheel gains traction.
I've heard the "piston slap" I always thought it was a ping type of noise, like temporary ignition timing off a little. I didn't think it was mechanical though. Only 1 or 2 knocks on start up. Not a real problem.
Both were easy to spin the rear tires though. That one hasn't gone away. That's a problem you have to look out for.
