I took apart my chain the other day (with chain tool) and cleaned it, and put it back on the bike. I noticed a stiff link (the one I had taken apart) so I bumped it with the chain tool and lubed it some more and it seemed OK. I rode it around a little bit and decided things were fine. Then I'm riding to work the other day and notice I'm hearing this "click click click click" sound that seems to be coming from the back of the bike - the chain skipping through the derailleur or on the cassette. I'm also having gear shifting issues (skipping up or down a gear, not settling into the right spot). It seems like it must be the higher cadence (high 80s-90s) since it didn't happen just tooling around the driveway. I checked the chain again last night. I spun it around on the bike looking for a skipping problem but couldn't find one. I tested each of the links by hand to find a stiff one and couldn't find it.
Any solutions? Any way I can find this stubborn chain problem? Thanks in advance.
EDIT: This is on a '92 Trek 1200, so it has indexed downtube shifting, and an 11-23 7 speed cassette (still the original one I believe).