I've seen two approaches to levelling a 3500:
Raise the front (via spacers or new coils)
Lower the rear (via shorter blocks)
If towing, especially from a hitch in the bed, is a concern, lowering the rear may be the answer to address any clearance issues. There is a kit from Dodge that does this and preserves the necessary pinion angle on the rear end.
HTH, Duane