thats the adjustment at the post. simple with fender off (ya just align to the cab), but doable with on.
open the door, loosen all 6 to the post. jiggle the door forward. jack the front of the door up to where the lower edge looks like the right height for the sill. tighten one top and one bottom. gently close door.
if your lower height is correct and you need to move the door forward or back some, leave one of those 2 tight as a pivot. loosen the other, move door, tighten bolt. reverse process, leave that one tight, move other in. you may need to do this a couple times. to make these minor adjustments it's best to have the door as closed as possible. say if you need to tighten the gap up top, loosen that top bolt, put floor jack at bottom back of door and jack it.
there are special wrenchs for this. but i generally just use 1/4 drive stuff..
if you have in/out issue thats the bolts to the door, far easier...