Serious problems with my e150, crankshaft position sensor

Hi, I've been fighting a misfire problem with my 2000 E150 with a 4.2 v6. The check engine started coming on in November and the engine would misfire, shake and stumble at high speeds. We replaced the cam position sensor and the check engine light went out for about 3000 miles. It returned in Dec and the misfire returned, we replaced it again but the misfire continued. We replaced the plugs, wires, fuel filter, air filter, checked the coil pack, all is ok. The check engine light returned again and its the cam position sensor again. We replaced it but the light continues to come back on. At this point I don't believe the sensor is the culprit, we checked wiring to the pgm and tested, we cannot find any obvious problems. We scanned the engine with a snap on scanner and found the timing will jump from 30 degrees at 2500 rpm to 16325 degrees at 3000 rpm. I think the pcm is losing sync with the cam position sensor, if anyone has had these problems or similar problems please let me know what you did. I am suspecting the pcm may be bad. I don't want to replace it unless its totally necessary...