Have a small storage shed on a slab and need to replace rotted-out sill
plate.

Unless there is a problem with high winds or side loads of some sort, why not
use construction adhesive and save all the aggravation? If your slab is typical
of most shed slabs the thickness is on the slim side and whacking away with
concrete nails isn't what you want to do to a delicate old piece of concrete.
HTH

Joe