You are pretty far North, so even your 'part-sun' is probably more shady then FL shade. Here in South FL i see Dracaenas in part sun outside.
Try giving it weak late/early part-sun (2-3 hours) for starters.
My Dracaenas in NJ were doing good in Western part-sun year round.
Generally speaking tropical plants with variegation require stronger light, especially further North.
