My experience is that the gypsum takes a really long time if ever to loosen clay soil. I have dug a huge deep hole. Take a post hole digger and dig as far down as you can stand. Fill hole with gravel. I also have put about two or three inches of coarse sand on the bed and till in. I have done both but tilling is a ton of sand alone has worked well. Sounds like you have a big problem.
Al's Manini Farm