Factory install on lower chrome panels, likely but not really, anything is possible however, more like a dealer install/ offering, as to pad the final sales, there wasn't much for a dealer to add to these trucks before final sales, my guess PO install as these kits where big for the after market(s) guys to sale and a lot of the older crowd "at that time" really liked that "garnish" like the bed rail caps, Auto Vent Shade products i.e. rain gutters, bug shields etc...
Those are really bad for holding and keeping water/ road grime etc... behind them and causing unwanted problems i.e. rust. There held on with the famous 3M double sided tape, depending on your patience, and good heat gun, a plastic pry tool, they will come off fairly easy and "should" not take any clear or paint with it, I use the heat gun and fishing line method when debadgeing any vehicle with very good results, any residue left is removed w/3M magic eraser wheel, buff and a good carnauba wax job and call it good.
I love the pinstripe on yours, have been debating this on mine with the 2-tone paint job, just have to figure out, chevy orange or red 2 stripes w/top being 1/4" and lower 1/16".
When my Dad had his 89 K2500 ext.cab step side, it was only a month old when I installed the lower chrome rocker moldings, chrome bed caps w/ the chrome tubing on them and the 3 bar chrome roll bar with 6 KC lights on top, and 1 bug shield and silver pin striping and the color of the truck, red with that burgundy interior, man he loved that truck!! He was the cat's meow!! At least thats what Mom said LOL! Man you could see him coming 10 miles away!! Thanks for the trip down memory lane for me!!
Again, awesome looking truck, rock it as you see fit!! and your eye for detail is great!!