(Build 4142545 - early unlock for reviewers)

Until others conditions not properly hinted in the achievement description are required, there's a bug for the achievement "Maxed Out And Geared Up". I just completed the Apocalypse difficulty too and right before the boss i was able to upgrade the latest enchantment required from tier 2 to 3, making it all of my equipped stuff having 3 tier 3 enchantments each. The achievement didn't unlock. 

You can see the 3 gear pieces in the screenshots attached.