spoiler alert: i linked this
OT?: MGOSTORE T-Shirt Length Question
I can't comment on the medium lengths, but I'm just shy of 6' and the larges run normal to long. Definitely not short.
edit: this may seem like a silly idea, but you might want to call Underground printing and ask an employee if they know the official length or if they could go measure it for you. Might seem like an odd thing to ask, but 1) they are probably bored anyway, 2) it's their job to sell them.
American Apparel shirts are generally longer and slimmer.
American Apparel and Gildan are prone to shrinkage. Also American Apparel runs pretty small. I'm 6'2 and slim as well and I have to get larges because the mediums are too short.