Yep, that's it. The vacuum line from it to the throttle body was pretty shredded, so I replaced it. Made the truck run better, but didn't solve the problem. Just went out in the snow and cleared the codes and rechecked them (11/11) and it still does the same thing.

I'll try to get downtown over the weekend and get a manual to see what the ECT (and other sensors) should measure and check them all. I'll keep you posted.

 

The problem turned out to be a bad throttle position sensor, and all is back to normal now (almost.) Unfortunately, in the process of replacing the TPS, I split the coolant line that runs to the throttle body, so now it makes a handy lawn sprinkler.

Thanks EPNCSU2006 for all your help.