Has a rebuilt engine 351ci 5.8 liter. The truck sat for 4 years and I have put tons on money into it. A couple months back I had problems with it missing (Vibration) and loosing power. I thought it may have been spark plugs and wires so I changed them, it didn't help. I took it to a mechanic shop and they changed 4 of the fuel injectors and it ran like a champ. Now the problem is reoccuring 2 months later. By changing only 4 could that have caused the others to go bad? What else could be wrong?