I don't think I would rebuild I would upgrade. I am getting really close to starting my ZF6 swap. My trans is so loud above 45mph I don't even want to drive it on the highway.

I say go NV4500 or bust!

 

to be honest, dan, i still think the ZF is way overkill for your truck & how you say you drive.

i had one last year (ECSB dirtymax) that ran for a whole week, but in the 1000mi i got to drive it, i realized quickly that the 3500 gearing & pattern is a lot more comfortable/natural for DDing... that & your truck ain't even that big or powerful, so the hardest thing you've got going on it right now are your tires & 4x4 launches.
but at least it didn't whine.