Hello Sandra,
yes the GN does rise towards the backscene and the offstage curve, although where past the flat crossing it starts to rise I wouldn't like to say offhand.
Trains can struggle up and round there in either direction if not driven fast enough as you quite rightly say. It often caught out sedate GN drivers.
As far as I am aware, no gradients have been altered since the original construction, and the GC yard does have a distinct gradient to it!
As for the baseboard legs, yes many are packed a bit, but that was to keep the layout level as the floor has moved a bit over time.....I'll tell you the history of that sometime if you want to know.
Pete Hill