Quote Originally Posted by lex_achter View Post
The pedals do turn when I spin the tire and the cassette seems stiff but I don't know how loose it should be or how it should spin.

I think this is probably it because it feels fine when I'm pedaling on a flat surface. It's just when I try to coast, I may as well be holding the break.
Have a bike shop look at your rear wheel. Either the spoke protector (do you have a spoke protector?) is rubbing the cassette or the freehub is not functioning properly or is almost shot. Or maybe there's debris jammed behind the cassette. If you took the rear wheel off your bike and gave the cassette a hard spin, it should keep spinning for at least 30 seconds.