Welcome! 6" lift will be a good amount of lift. You're fuel mileage will drop at least 4+MPG also. But hey, smiles per gallon is more exciting than miles per gallon.
I'd search around and compare the stance to both of them. I had a 4" on my last Chevy truck, and it was more than enough after...
You don't want to piggyback over a custom ECM tune. That's the old school way of doing things back when tuners didn't have the know how or access to the correct tables to create a good tune.
I'd like to see GM's book hours for that trans drop to replace the belt. I've heard a few say it's a bit easier to do it GM's way rather than how Ford does the new 3.0L.. so, pick your poison! :D