To me it does not have the "flash" that you typically see on unc
Morgan dollars. On unc dollars the luster should be "unbroken" and the "flash" should just jump out at you. The more coins you look at, the more you'll see what I'm talking about.
I pegged it at 55 because I've seen thousands of AU coins just like it. Be especially careful with 79-0 and 84-S dollars. There are thousands and thousands of those dates that look just like your coin. People try to pass them off as "Uncs" all the time. (I wished I had a dollar for every AU 84-S I've seen in 2x2's trying to be passed off as "unc"!)
Use this graded coin as a learning tool. Carry it with you to coin shows and learn from it.