I had 3 avys before my burb. All you need is on the above mentioned forum, as well as this one. While not near as active, a search will give you all you need to know there.
The avalanche is essentially a suburban, and the mechanical parts are the same from the front seat forward on the 07-13 (as is a tahoe). The frame and suspension are also the same, so most suburban advice crosses over. If you choose the 03-06, the front clip is the same as the silverado of that age, so the truck forum (gm-trucks.com) would apply there. The original 2002 is its own beast with limited part availability, so I would not go there...
Know the bed is not waterproof, but will keep out most water. The best mod is the homemade bed slide - I missed it so much I made one for my burb, but it wasnt the same, and I needed the rear seats. My 13 held its value better than any vehicle I have owned since they all were black diamond special editions with painted sail panels - the 12 is probably priced better, and can have the same features. All LTZs have the autoride (similar to magnaride) with rear leveling air shocks. They are expensive to replace, and last only 60k miles or so. The back window frame will crack, but liquid gasket fixes it well. Were I to buy one today, I would get a 12 or 13 Z71 as they are the easiest to maintain. You got me thinking I need to get another one now...
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