My 2000 Durango 4X4 with 4

My 2000 Durango 4x4 with 4.7 liter engine has an intermittant 'check engine' problem. Some days the engine runs fine. Other days, the check engine light comes on and the engine 'misses'. I had two different mechanics run diagnostics on different occasions. At one time it indicated code P001. On a different occasion it pulled up codes P001, P002, P006, P007, P008. There was also a footnote on one diagnostic that voltage fluctuations of 0.02v in the TPS could cause the PCM to indicate an injector problem. So far injector #1, TPS, and the alternator (due to alternator failure) have been replaced. The mechanics have not been able to isolate the problem. I can't afford to keep replacing parts to find the problem. Any ideas?