Deacon is this bike a single speed or a 10 speed? most multispeed bike have 2 small fingers held in with a round wire clip or thingamagigs that engage to power the rear wheel they might be sticking and that will account for the slipping. heck I don't know that those parts are called so I had to get western with the words can I have a blue star?

. single speed last time I took one apart I was 10 or 11 so you can take the star away I don't know much about them.
Norman