I do miss the simplicity and low cost of running, but my back and knee are definitely happier on the bike.
Hopefully it's just a cable adjustment for you. Either way, I'm a sure a pro will take care of it easily. I finally got to use the big cogs on my MTB last weekend. Things shifted just fine noodling around the neighborhood, but it wasn't right under load. I love how MTB shifters have the barrel adjuster right there at the handlebar, so I was able to tweak it on a hill.
Speaking of, had a blast on Sunday riding one of the not so far away MTB parks. There's a natural bit of undulation in the ground there, enhanced by some trail building, so it was a ton of fun to actually do a little climbing. I rode the greens, connectors, and a couple blues and didn't crash at all, so that's victory!
After having only ridden singletrack on gravel bikes, I still can't get over how stable and capable my hardtail is. I put flat pedals on it because I thought it would give me some confidence, but I'm finding they're giving me more problems than assistance. Gotta try it with the SPD's next time.
And those in the know understand that the correct number of bikes to have is n+1.