I have a 2003 Z71 (1500, Ext Cab) and I use this truck off road all the time. I only have 33" tires (no lift, they clear fine). But I want a solid axle. I keep hearing that it's a weak truck, but I have seen them run 40"s w/o soild axles, just a lot of body lift. I want to run 38"s at most, I just want the added stregth and travel of a SA. If there is a kit, or if anyone has an idea of where to start I would appreciate any help I can get.  

I have done alot of researching on this subject and for your year model you might start with Cage Offroad. They offer a very well designed kit, but it is a coil kit with 2-link suspension. You could also try:
Offroad Direct
Offroad Unlimited
Sky Manufacturing

These are just a few. hope it helps you.  

Thanks! Offroad Direct makes a kit for it. So now if there are any suggestions for which axle/diff and so on that would be awesome. There site says the parts list isn't complete so all the little bits aren't on it. I'm pretty much lost in this stuff. I appreciate it very much.  

And what about front and rear gearing? I'm not 100% of what it is stock (3.73?) but I know they have to be the same. And I plan on using a Ford Dana 60 up front, so will the factory rear end be strong enough? Maybe I should just wait and see what they do with this new Z71 project truck... the Marine Corps needs to give me a raise!

And another thing... I have push-button 4x4. Got a feeling thats a problem