Over the winter i do some major service of my bike. I checked the chain, with the Park tool, and it was under .5% wear so I reinstalled it. I've put about 500 miles on it since and a few days ago it would occasionally jump a tooth in the 4th and 5th largest cog. It was suggested that maybe it was a tight link so i checked the chain and didn't find any. So at my son's suggestion I changed the chain and .... not only is the problem resolved, it shifts so much smoother.

I'm glad that my LBS not only had it in stock, they also have a decent online presence and I got it for the online price... $45 for a Sram Red 22 chain.

I'm just going to replace the chain every winter, even if the Park tool says it's under the .5% mark.

BTW, i hung both chains from a finish nail in a ceiling joist to get the correct length to cut and the old chain was 1/3 of a link longer.