Nothing that I know of as you describe. Personally I think it is better than having to get out and lock hubs when 4x4 is needed. As for performance...I doubt you would see many gains. Just look at Michael Tomac running 12 second 1/4 miles (in 4x4), as well as all the reports of 20+mpg out there.
Today I noticed that the front drive shaft turns freely on my 2003 2500HD D/A CC, while it was parked in 2wd. I was changing the oil and looking for grease fittings and I was able to turn the front drive shaft by hand only to discover that there aren't any zerk fittings in those universals. Oh well.
So the previous post by jbplock is indeed correct!
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