As
@rgosart said. X/X is referring to inches of drop front & rear respectively.
Stock keys can be adjusted down a little without a noticeable penalty to ride quality. How much exactly is up to you... I'd say @ ~1" drop ride quality isn't bad. If you want more you really should go with some drop spindles.
But why take my word for it, it costs zero $ and however long it takes to jack up the front end and back off the torsion bolts a little...15 mins max?
The rear can be accomplished easily with a spring swap. And some more work if you have air ride.
We should probably start another thread about lowering your truck though before I write a dissertation on lowering in a thread about tire recommendations....
