I installed E fans on my 04 Yukon last month, using LS1fans.com harness and EFI live that I bought from Black Bear to activate the PCM pins myself.
My yukon already had the big radiator.
Bought the fans from rock auto, and they are the higher blade count OE ones for an 08 yukon.
The harness from LS1fans.com was a real good quality harness with labels on everything but there website is not updated for directions and there were no pictures for the install instructions on there website. I even email them with a question about the ground wire coming off of the passenger side fan plug, to see if there was an existing bolt you use or if you had to make your own hole. There reply was very vague so I wound up making my own hole to ground.
Only other problem I ran into was I had no bolts for the fans to go into the top of the radiator core support. I didn't think about it and I didn't see it mentioned in the e-fan thread before. So I just borrowed one bolt out of the radiator for now.
And I am still using the stock Alternator with the stock pulley for now.
Also at the same time I installed a Airaid MIT tube for an 05 yukon.
Still it was fun and makes the truck look newer and gets rid of the loud clutch fan in the summer.