But then it was time to spend a little money.
Some tonneau cover manufacturers claim as much as 10% mpg improvement from a simple cover. Bull sh!t, but, it can't hurt. I wanted one to protect my cargo anyway, so it made sense to buy and install one more or less right away after I bought the truck. Installed it at work as soon as it arrived:
One thing I always do to my vehicles is install a badge-less front grill. I dunno why, I just really love a stealthier look. It also makes fabrication of a partial grill-block that much easier.
First, pull the grill shell / front clip and cut out the stock GMC part.
Then fit the replacement:
I didn't get pics of making the grill block itself. I cut some abs plastic rather meticulously until it fit nicely and just zip-tied it in behind the new grill. I estimate the block-off of the main upper grill opening at around 70%. Plenty of airflow hitting the radiator still; I may block the lower openings if I can figure out a clean way to do it (no duct tape for me).