Is there a difference between 2wd and 4wd transmissions?
 

Starting my build on my all stock 04 1500 4x4 and the stock 4l60e shifts hard into 2nd at low rpm and last time I got on the throttle it bounced between gears. I was planning on having an efi live tune done but now I'm fearing that the stock tranny might let go if I do. So I'm starting to look into built transmissions and was wondering if anyone on here could help me out in finding out if there's a difference between 2wd and 4x4 trannys

Yes they are different. They have different output shafts and different tailhousings. You can make a 2wd trans into a 4wd and vise versa but you will have to tear it apart and replace a few parts.