My 99 GTP is having misfires on cylinders 3, 4, and 5. Cylinder 4 is having about twice as many misfires as cylinder 3 and 5. The only thrown code is for random misfire, it never specifies cylinders. It only causes problems when I am hard on the gas, gentle acceleration works without issue.
This problem has persisted for around two years now and hasn't gotten any worse. I've tried attacking the problem a few times and can confirm with near 100% certainty it is not a plug/wire/coil pack problem nor is it a vacuum leak. I took it to a GM certified mechanic and he didn't find the problem but suggested I change the injectors, is this likely the problem? How can three injectors go bad at the same time (I think it works this way?) ?
The best advice is to take it to a junkyard but any other advice would be appreciated, thanks!