Yep, it was the upper radiator hose, but it was a pain to fix (for a hose).
I had to remove the air hose to get to it, and then I had to twist my arm
into a really awkward position to remove the clamp attached to the engine,
seeing as how I had to use pliers to clamp it open. The end attached to the
radiator wasn't much better, as I had to unscrew it sideways. After I
finally got the hose on, I filled up the coolant tank with antifreeze, and
like an idiot, immediately drove to the nearest Arby's.

I am an idiot.

It took me a while to figure out that the engine was overheating because it
needs more coolant than a single tankfull to operate. Fortunately, I didn't
let it get too hot before I added some more and let it circulate.