Thanks so much everyone for giving me ideas of what to look for! I did a search on the bike and it appears to be an older bike from the 70's or early 80's (most likely the 70's). It has not been rode and setting outside for 1 1/2 + years, it was under cover so it wasn't like it was being rained on during that time, although it was exposed to moisture. When I said the chain "doesn't feel tight" I mean to the point that it would cause the wheel to lockup, the tension feels normal.

I did notice one time when this problem happened if I would pedal "backword" the chain would become very slack on the top dropping down and touch the chain stay. Of course after I rode it the problem would quickly go away and you could pedal "backword" with no problem being slack. Another time it happened and I spun the rear wheel the complete drivetrain would spin (rear wheel, chain, cassette, & pedals).

I will look into it further and let you all know what I find. I have a link below to a picture of pretty much what the bike looks like. My bike does not have the chrome "dork disc" shown in the picture (mine has non at all), everything else is pretty much the same. This is a pretty nice old bike that seems to have some soul. I think with a little TLC this will be a nice vintage bike to have in the stable! https://www.google.com/search?q=brid...Ian7MNAUz-M%3A