A couple of days ago, I had my truck's oil changed at a quick lube place. The morning after, I saw a quarter-size spot of oil underneath. As far as I can tell, it hasn't leaked anymore. I had the oil gasket fixed a few months ago on the truck, so I don't think that's it. Is it normal for a truck to kick out some excess oil after a change?

No it is not normal. However they could have spilled oil on a cross member when removing the filter and this could drip the first few hours or so.