Hahaha, I used to have to shop at Big and Tall back in the day. Luckily I'm small enough now to shop at real stores. I have a huge problem because I have to always try things on since I'm an XL in the shoulders/chest, but a large in the waist area. A lot of my clothes have become pretty baggy in the midseciton since I lost weight, but what can you do? I'm also 6'3 and some shorts are also too short. Good luck with your search, I wish I could even take the chance shopping online.
Oh and Gap shirts are all cut differently, some fit differently than others because they come from different factories. Even the same style, color and size vary as far as fit goes.