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That is up to you!
The idea of a leveling kit is to lift the front of the truck so that it sits at the same height as the rear. If this is the way you like it then you don't need any lift blocks.
A lot of people add rear lift blocks also so that the entire truck gets lifted, but then you still end up with the rear of the truck sitting higher than the front.
Either way works fine, it just depends on what you want.