The tire size will dictate the gearing. 33s have and can be done on stock gears but you will notice a difference. The lift height has nothing to do with it. But on what height to go with depends on whether you want to step up in tire size later and what clearances you want. If 35s are in your future go with the 6.5", but if you're gonna stay with 33s and want more stability on road and off the 4.5-5.5" will be better, although some trimming will need to happen but 33s will need that anyway since these wheel openings are undersized.

Rcv shafts are the ultimate axle shafts you can get for the Dana 30 but the price makes them not feasible in my opinion. You could probably get a Dana 44 and swap it in cheaper. But if you want to keep the 30, they probably will save you some time changing broken u-joints and shafts if you're rough on them.

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