Can you get a G56 tranny to fit into an 01 3500? If so, how labor intensive & expensive is it?

I would try to find a nv4500 or nv5600 before the g56. I'm not a big fan of the 56's because they have a lot of problems and can't hold up to the power. Also I'm sure they 56 is different length and you would have to find a t-case that would fit it, then different drive shafts. I'm sure you could do it but why not find a trans that you know actually fits in the truck

Yes I have read a few threads on G56's into 2nd gens, as mentioned it needs different shafts and mounts. The G56 is good up to 500-600 rwhp, but that's about it.