I'd get ahold of the leveling kit manufacturer. They can probably recommend a shim, or other fix for the vibration. BTW, your rim width is a bit narrow for those tires, especially the 325's you 1st put on. I don't recall any 285/65 18" tires as stock. Stock tire size for your truck w/ 18" rims should be LT275/70R 18E. Either way, you probably didn't change total dia much more than an inch (bigger). The more I think about it, the more I'm thinking it's a tire issue. I would find something else you like in a tire (through the tire center you're using), then try'em.

 

yes it did

 

yes it started right after i put a 2.5" readyift leveler kit on it.. I just did the blocks above the shocks, i did not put a drop downbracket on