Aluminum Drive shafts
 

is it only the Crew cabs that come apart or does the extended cab one come apart to?

Both. I believe they are the same wheelbase and use the same shafts.

ECSB here n blew it up .. Its when you unlock the top end limiter that they fail .. Some are balanced better than others and dont vibrate but recently other members who never felt a vibration blew theres as well .. Just a matter of time before that flimsy ass cardboard lined stock aluminum shaft gunna let go .. If stay on the limiter you shouldnt have any problems .. You hope:dewey:

i here its over 100mph. witch is nothing for my truck

This makes me wonder, how do the nbs rcsb 4x2 drive shafts hold up?

Several members here have already lost both the aluminum and steel models at high rpms. Most RCSB have 3.08 gears and in factory form don't turn much rpm, but start exceeding the speed limiter or changing gears and things get hairy.

I have 3.73 (was 3.08) and vibration starts at about 115

This the reason I went to a larger aftermarket driveshaft. Factory driveshaft felt like a pop can next to my new one.

iv hit 124 according to EFI Live and felt no vibration. truck was nice and smooth

But your 4x4 ds is much shorter than a 4x2 so it has a much higher critical speed.