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[Dr.Evil]

Why wouldn't pistons, rings, & valves get hot just like the turbo? They're exposed to even hotter combustion gases than the turbo. And I would expect pistons that are running 800-1000 degrees F WILL cool down when exposed to combustion gases running 300-350 deg. Plus You still have the oil jets spraying 180-200 deg. oil on the undersides of the pistons that will cool them, Plus heat transfering into the cylinder walls through the rings...plus the waterpump circulating water thru the heads, block, & oil cooler...
Have You ever noticed what happens to a NEXTEL (Winston Cup) Car during qualifying? The water or coolant that blows out of the radiator overflow when they kill the engine instantly when they're across the finish line on the last lap? Don't You think Your PSD would and WILL do that on a hot day at full load and You shut it off without a cool down? FRANKLY, if it's really hot and Your working Your truck hard like pulling mountains close to max. GCWR I don't think a half hour cool down is too long. It's not like wet stacking is going to be a problem.
I won't comment about what You remember reading in old truck Owner's manuals but I remember what I've read in Mine. [img]/ubbthreads/images/graemlins/grin.gif[/img] I've seen many N/A gasoline engines running with the cast iron exh. manifolds glowing cherry red. That's just about the temperature that takes the temper out of piston rings and causes them to not seal properly... And as far as what Owner's manuals say or not being good operating practices for an engine..... Remember they want to get You through the warranty period is all...