I agree that fueling may be @ issue. Scanning the ALDL port will give you a pretty good idea how it is running. (O2s don't always throw a code - at least not right away. They can be failing or getting weak long before failing completely to cause a code (I've found).
Besides O2 function, you will be able to get a dynamic evaluation of ALL the sensors: a good place to start!
I don't want to start speculating until we see what the scanner says first. JMO.