Do the problems return with the O2 sensor hooked up? If they do, replace it. (NTK, or Denso only please, don't bother with Bosch, our trucks don't really like 'em.) If the sensor is original, it probably wouldn't hurt to replace it just on general principles.

 

Well the truck is a plow truck so if it works with it unplugged I'm not going to buy one. The thing I don't understand is how is was running like **** one day and the next it runs fine.

 

Probably the O2 sensor.... they have some rather odd failure modes, that don't always set a code.