Based on personal experience, I'll bet that your plugs, fuel pump, fuel & filter are fine.
Remove, clean and re-install the EGR (Exhaust Gas Return) valve located on the rear of the engine. It gets stuck with carbon buildup and will cause it to stutter, miss, idle rough or just sounds terrible.
I've had to do this on not only mine but my dad's and brother's big blocks. I scrape off or glass bead (sandblast) any carbon or buildup, lubricate with WD40, make sure push rod is free, seal with high temp 3M and reinstall or go to NAPA and purchase a rebuilt one (had to do that for my dad's 460 second time around).
Before you go and spend a lot of $$, R&R the valve and try it out. It is not a difficult job.