I will state this - local dealers aside and end links as well - I have never enjoyed a vehicle as much as this truck. I've owned some nice vehicles over the years as well. My extremely finicky wife likes my trucks ride and interior better than her 19 Acura MDX (and so do i).
I've never had a single issue outside of the sway bar links being loose (local shop tightened and didn't charge a dime as it took em 15 minutes to diagnose and tighten). Full expect that the bushings in the links are the culprit. Will know once they arrive and are installed. Candidly - they are a $27 part when discounted and shouldn't be but an hr to install.
My truck runs as nice, and quiet as new and I've only completed oil changes and end links tightened.
BTW - I also live at 8000 ft elevation and overall MPG avg is sitting right about 19. Im in the Mts and up and down to get anywhere.
Its very possible 1 bad shock landed on your truck or something else happened - I guess hard to say but sounds like you have found a good tire/sus shop that's gonna address it with. Keep the faith! Hope you have a good outcome.
I researched shocks/leveling ad nauseam. btw the 2 the reviews are nearly the same. Some like the bill better, some the Eibach. Bils out of stock and Eibach are mfg and assembled here in the US and in stock. Same price really and same basic features. Ill post a review once installed and a few drives under my belt. I also had some great service when asking questions about ride quality, which springs (stay w stock or go with theirs), install, spring perch location etc...