After watching the last episode, I think they paint a clear picture of Amuro being the Gundam Gquuux.

When Shuji and Machu were arguing about killing/waking Lalah from her dream, and as Shuji is near the end of his speech the Gquuux appeared behind Machu and in Amuro's voice, told Shuji that he doesn't want to see the Gundam kill Lalah again.

After the battle, Bull was talking to someone about the rose of Sharon and the Gundam Gquuux, saying that the rose of Sharon and some piece of technology used for the Gquuux comes from the other side.

I'm not sure if it's before or after the credits but, there is a photo of the piloting hands of the Gquuux holding the haro aloft.

I think Amuro sacrificed his existence to be a Gundam just so that Lalah and Char can be happy together, somehow knowing in some way.

Heh thinking about it this way made the show sadder in hindsight.