Newbie wheel, tire, and suspension Question

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I have researched the site and I have yet to find the answer to the following question. I was wondering about putting 20" wheels on my 05 2500HD 4x4 when it comes in and I was wondering about what tire size I needs? The wheels that I am looking at are Divno Trench 8. They are 8 lugs and 20X9. My two main questions are what size of tires should I go with since I want to keep my load rating of E due to the fact that I will be pulling a 10000+ boat and will I need a lift kit for the clearance? I would like to have at least 65cm sidewalls. According to my calculations this would make my overall tire and wheel combination around 45". Does anyone run this size and will it work. Any suggestions will be greatly appreciated.