What's wrong with my truck?

[snap_knight]

Recently I began having horrible gas mileage on my 2001 S-10 pick-up truck (15 mpg) . I added the recommended amount of Chemtool fuel injector cleaner to help clean the injectors to see if that was the problem. After about a half a tank, my truck began to miss something terrible. Thinking that some of the crap broke loose, I added some more on the next tank full. It helped for a little bit and this morning, it ran better than it has in five years. This afternoon, it will barely run. It's missing so bad that I can't even go anywhere. What's up someone?