Test O2 sensor, test Air Flow Meter (AFM - http://www.4crawler.com/4x4/CheapTricks/AFM/index.shtml), send injectors out for testing and cleaning (http://www.4crawler.com/4x4/CheapTricks/EngineMods/index.shtml#Injectors) , hook up a fuel pressure gauge and test the fuel pressure, etc. Basically test and eliminate one thing at a time.