J Barca's plug work is on an '05 modular V10. That is the three valve engine. The OP's engine is pre-2004 so is the two valve modular. There may still be plug removal problems but not as likely.
If the OP doesn't want the hassle of plug replacement, I'd suggest to try replacing the COP on those cylinders that are not functioning. I have 180K on my truck with the original plugs and a single COP replacement got it back into good running condition. I know I'm overdue on plug replacement but the dealer is going to get that job.
