Was my dad trying to talk to us just before he died?

Possibly: He may have been trying to talk to you and for various reasons he may not have been able to speak.

You won't know: Before death, people may become more lucid for a moment. No one knows why or what it means in the grand scheme of things. Move on, forgive as you need to, cherish the good times -- and be glad you were there for him whether or not he tried to speak to you.

Probably.: People often describe a brief moment of lucidity right before someone passes. He may have been trying to speak, and he certainly should have known that you were there with him.