95 Buick Regal GS

Buick Regal 3800 misses noticabel high gear under lite to moderate load .Getting code Po321 Ig. dist. engine speed in the code history, however current code being set is PO300 random missfire dedected. Parts found faulty or dirty 6&3 coil pack yellow spark R&Red,spark plgs, inline F I cleaning, cleaned IAC. Come to find out car runs great intermitently , whenstarted no check engine light runs great, now onthe other hand car sometimes starts & we have check engine lite same mi ss i started with comes back. Thanks Good people hope you can help.