Anything over 1" lift shackles is a bad idea. It will lead to severely sagging springs. Your best bet will be building a bastard pack to give you another inch or so. As for avoiding an SYE, keep the suspension lift under 3" and set your pinion angle correctly. Some do 4" lifts with no SYE and have no vibes at all, but others do 2.5" or less and get vibes... So there is no gaurantee you won't, but a properly setup pinion and t-case angle is key.
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