Freshwater amphipod ID help? (Centre county PA)

I was told this sub also can help with IDing freshwater critters.

I found these amphipods in a creek in Centre county Pennsylvania, on a piece of rotting wood. They are quite gray in color, and up to about 1cm max body length. They have a very vigorous "flicking" response when taken out of water.

My best guess so far is genus Crangonyx, but I am not an expert and could easily be way off the mark.

Edit: Now leaning away from Crangonyx and towards Gammarus, maybe G lacustris?