Shouldn't be a sand issue. I know when I first got the washer, It seemed to pump, then stop for 5 seconds, then begin spinning. This is what it's doing most of the time, sometimes it's pumping, stopping for 5, then pumping more but not spinning.
The Drive coupling seems really easy to replace, so i suppose I can give that a shot first. I was under the impression though that if it were bad I'd be getting no agitation or spinning ever, is that not the case?