New guy problems

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Hey guys I'm buying an 07 suburban today and in the loan price I'm getting new tires . So I am trying to find out what size to go with and an looking to level it at the same time maybe a 2.5 and a 1or 2 and 1 . But this thing has air ride . Can anyone point me In the right direction so I can see what I need to add to the loan and where to get the leveling kit also will be adding Firestone air bags because I haul an enclosed trailer on the weekends

 

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I'm also wondering since it needs a compressor and front shocks if I should replace them with oem or get rid of it when I lift/ level . Any help is appreciated I did use the search button first