The 3.1s were not bad to work on. Believe me there are worse. hopefully you have access to a scan tool to help with diagnosis. I would check fuel pressure as well, not sure on the spec right off hand, but probable around 45psi. Also I would check the exhaust backpressure for a clogged cat. I have a homemade tool for backpressure, it's a old 02 sensor I beat out just for the threaded part and brazed an brake line to it so I could connect a vacuum hose to my vacuum\pressure gauge. With the gauge connected open the throttle anything over 1psi, there's a restriction. The no tools method is to just take the exhaust loose in front of the convertor and drive it to see if it runs better, or just remove the 02 sensor and drive it. Good luck.
