NV4500 but they're hard to find and junkyards want a fortune for them! I found one in a wrecked 99 silverado with a 4.8L and the NV4500. I wanted it really bad!!!! It had about 80K on it and they wanted $1,200!!!!! (For just the tranny!) I found another place that had one and they wanted $900. Still to high for me at the time
Now that I have the $$$ to do it, the truck already has a 700R4.
69rut's suggestion is good and shouldn't bee *too* expensive. Much cheaper than the NV4500's.