Odd problem

My truck has been running fine. This morning I go out to grab something befor eI head to school. I crank the truck from the passenger side. It was kinda chilly. The truck started, studdered, and almost died. After a couple of seconds it finally picked up and idled correctly. Well I let it warm up while I get ready. About 5 mins. I get in it and I have about half the power I should. Really noticeable loss here. Well I assume my cat or something exhaust wise has fallen off maybe. I pull into a parking lot and look under the truck, everything where it should be. I kinda panic. I turn the truck off and turn it back on. Now it runs fine, no skip and full power again. What could have happened? And why did it fix itself? I just want to make sure nothing is broken and I make it worse by driving it. I would rather know what the problem is and fix it.

Thanks!!

Just for those who do not know me, it is a 2000 Blazer LS 4.3 2wd.

May have been a stuck choke, how cold are we talking?...it could be a number of things. what I do every year along with winterizing I also wash the engine either while cold or while running and I coat everything plastic and rubber with silicon and I coat all mechanicals with some type of lubricant.
JM2C

Well it was cold for Albany, Ga. Maybe 40ish.

It wouldn't have been the radiator clutch fan not disengaging until you shut it off would it? Did it sound like it was a louder engine roar from the engine compartment than usual?

No, I do not recall a louder sound from the engine but the exhaust was louder than what it should have been though, which is why I checked it. But it went back to normal after restart.