Westover Air Reserve Base is a little to your west. They have several C-5A's assigned there. I once flew through there on a C-5 myself. The Air Force does something that they call "locals" which means they fly around for periods of usually 4 hours for pilot, and crew training. I would guess this is what they were doing. Sometimes they will get a 100 miles or so from their home base while doing this. Only speculation that is what they were doing, but my best guess.
Hope this helps,
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