[Billett]

I've always liked the 4l80 over the 6l80. Not that the trans is better, but its so much cheaper, just as capable in terms of power, and easier to tune.

As far as wiring harnesses, I got mine from Current Performance and the wait took a bit, but the harness itself is awesome. Very well made, everything is labeled and ran perfectly. $725 for one with an auto trans, fuse box, a/c, and the e-fan relays