I gave up on GAP many years ago, after I was addicted as from early 90s.
I ended up using the financial sledge hammer, Reiss, to crack the simple T-shirt fit nut. Reiss still make their T-shirts with the 90s slim waist fit and at a good quality. Though I have found Next slim fit range to be a good fit at a thankfully lower cost too.
Environmentally these tissue paper thin T-shirts that don't last are wrong. Its a race to the bottom in terms of mainstream fashion quality and environmental impact.