We've been through lots of types of limps around here, too. It's true, Pyrs can strain a leg or paw easily with that steam shovel digging that they are infamous for.
Most of our limps have been easy stuff. Pulls & strains should resolve within a few days with lots of R&R. Halley had pano as a puppy and it came & went periodically. It was treated with Rimidyl (short term) and a change in her food. If you have foxtails or other types of weed seeds that can poke into their feet, then it is important to look &
feel around very carefully for any sign of something poking into his skin and between his pads. Foxtails and all move remarkably fast, so it's important to try and find them within a day or two or they'll be entirely inside, harder to detect and remove. I would suggest that you have hubby gently restrain Yukon and distract him with pets & treats while you use a bright light to look carefully at his paw (especially in between the pads where stuff gets stuck). If you don't see any irritated spots, then I'd wash his paw (just in case he stepped into something irritating), and just watch it for a few more days. You're right about their pain tolerance, it is really amazing. You may be able to feel around on his joints more for any swelling or tenderness while you're holding him down, too. If he is breathing really fast, panting unusually hard, or wincing you'll know that you've hit a sore spot. Hopefully, it will resolve on it's own. Give him a hug for me.