tech help for lifting 09 sierra denali

[Steelrain]

Hi new to this site. I have an 09 Denali i just bought and was under the understanding that the truck had a 2" Rough Country leveling kit on it. That being said I did a lot of calling around and checking trying to find out how big i could go with tires. I have 20" Black Rhino Serengeti wheels. I was told I could stuff 305 55 20 under her, so I went with Dura Tracs from Goodyear. Now I have issues they wont fit!! Turns out I in fact do not have a leveling kit in it at all. To make matters worse I need to lift the truck to make them fit. I want to go with a 4" kit, and have been doing a lot of forum cruising looking for advice. I am aware of the dual Cardan driveshaft, and some people having vibration issues and others not. Can anyone offer advice or give me a number to a shop who has had good results doing this? Thanks, John.