I just don't think the latest firmware is stable at all, for me this has been the worst firmware, speed si completely random, one min speeds can be normal and others down in the ditch. So its all about consistency which d-link routers; 4500 and onwards have never been good at.
I just hope a new firmware is out soon, and I hope d-link know what the problems are and how to fix them.
Again, I think maintaining a stable connection and the 3 day disconnects are somehow related, lets hope a fix is coming, because I can't keep buying new routers; in a hope that a newer model is better; because it isn't.