"God's eternal present" - I think this is a problematoc phrase.

There is no "now" for God. Temporal things exist in a changing now. Being outside of time, I don't think we can thinkod's existence as an "eternal present". There is no "syncing up".

"He sustains things at one moment... And then sustains things at another moment." This seems to be putting God in time. For God, all things are present to him but not in the same "present" as in the temporal sense, lest we slip into making God temporal.

And that is exactly what happens with presentism. There is only one moment, the present. So he can only sustain the present moment of time and the things which exist at those moment as its the only thing that's actual. But they would constantly begin and cease to exist.