A friend of mine broke his driveshaft on his '02 Z71 when he got in a bind and it just twisted. So does anyone have a suggestion of a stronger one besides the aluminum factory shaft...which will probably be expensive as all get out from a dealership.  

I'll bet they has big tires and stock gears too! A permanent fix here is replace drive shaft and regear axles to deeper ratios which limit/reduce average driveshaft torque. Many never even give the slightest thought to strain big tires with stock axle gears place on drive line. A drive shaft failure is a warning that you are exceeding limits of drive train. They act kinda like a fuse in that they are designed to fail before splines strip, tcase internal components fail or pinion heads wring off. (just like axle shafts are designed to break before "pig" does) The only real true fix here is not a bigger stronger "fuse" but rather regear axles to get average drive shaft torque levels down within design limits. Failure to do this can result in a far more expensive repair in future.  

Actually he was running 31" tires... Mastercraft Coursers I think... some kind of off-brand A/T's. I really don't see how it happened, his tires weren't in a bind or anything, just spinning away in the mud. The fun part was pulling him out with part of that shaft sticking into the mud.  

There was a time long ago when 4x4 trucks were geared properly from factory but not anymore. Most have car like gear ratios, rides and chassis and they put a label on it like Z71 and it is supposed to suddenly be HD.  

Why does everyone hate Z's?  
I do a lot in mine and it hasn't broken... yet.  

It is not a question of hating them it is just that some like me have been around for a long time and remember when 4x4 trucks were really trucks per say rather than car trucks today. Today a GM truck is a some of parts from lowest bidders and it get worse with each model year as with each revision they strive to make it cost less to build them. If I had not been around as long I would not know there is a difference in what a 4x4 used to be but I have and I do.  

I suppose your right... but I'll keep wheelin' mine until it won't go anymore. But back to the point, thanks for the advice and knowledge on the driveshaft subject