'91 usually fast and responsive, but slow today

for some reason my truck wasn't running as well today, usually it accelerates fast and stuff, but it was kinda slow and not very responsive. It's had it's days like that before, and then later in the day, or the next day, it will be fine. Why does it do this? my first guess would be because it was cold out and the engine hadn't warmed up, i was late for school so i just started it and went.

try adding gas line antifreeze, and see if it helps

Ever done a tuneup?

Ever maintained it at all?