I can provide you with everything needed for the GMT900 upgrade except for the hydrobost unit, but I also need to know the exact model year of your Tahoe to get the confirmed part numbers for the rear brake parts. Right now R1Concepts is offering a 15% off sale through tomorrow (Wednesday Oct 23rd Thru Midnight PST). To use their online catalog for finding what you need, click the link in my signature to view their catalog, use the year make and model drop down menus to look up the front brake parts of your choice for a 2008 Tahoe 4x4, then go back through and look up the parts for the rear for your year model. Then during check out, use Promo Code FFDISCOUNT during check out to obtain the 15% discount.
That being said, there are a couple of choices for rotors and pads. Because of the size of your rim and tire package I highly recommend their Premium drilled and slotted rotors matched with their Posiquiet Ceramic pads. I have installed and sold this combo for literally hundreds of 1/2, 3/4 and 1 ton trucks over the years and have never once heard a complaint about quality, performance or longevity.
Anyone that would like me to prepare a quote for you can send me a Private Message here on the forum and I will prepare that ASAP.