I have the same issue. A trim is not needed unless you have a serious amount of knots on the ends. Trust me, I cut off 6 inches of hair last week and I still have the same problem of my ends locking when I air dry or blow dry. I too have 80% or more shrinkage. It is important to first get your hair almost straight before flat ironing.
I have been experimenting today, literally, and I found that blow drying on almost-pretty-darn-near dry hair in small sections with a very soft round boar bristle brush on the ends help a lot. The hair should have heat protectant and a leave-in applied before air drying. The small tooth rat tail comb doesn't do a good enough job separating all hair strands like a brush would. And right before I blow dry, I added a bit of chi silk infusion, not because it is miraculous, but because it provides a bit of slip when brushing the ends ( I want to cause minimal friction).
I didn't get to try this method on my entire head yet since I was doing so many combos of blow drying-flat ironing, air dry-comb out-flat iron, flat iron on low-comb out-flat iron high, etc.
But I hope to try again next week. Good luck finding what works for you and please keep me updated on anything you discover.
