P0300 code Fluctuating RPM's worst between 1500-1800

Car starts fine. When accelerating when cold, engine chugs. Rpm's fluctuate while driving from a stop and at cruising speeds even with cruise control on. Fluctuating rpm's can be accelerated out of. When engine warms to operating temperature, the car can then be shut off and restarted after a few minutes and the fluctuating rpm's are no longer an issue and the car runs fine.
Have replaced spark plugs, plug wires, distributor cap, rotor, throttle positioning sensor as well as fuel filter. Have cleaned mass air flow sensor and EGR valve. Have taken off distributor cap and it does not seem like the rotor has any side-to-side play. Has a little up and down play. I noticed when I took the distributor cap off that one of the hold down screw holes was stripped out, so I installed a repair kit to fix that. Have tested fuel pressure. At start up with fuel pressure gauge on it has about 53 PSI and at idle has about 55 PSI. When you hit throttle it will go up to around 62 PSI. After shutting car off it holds pressure for at least twenty minutes, have not tested past that. Have tested the TCC by lightly pressing brake while rpm's are surging to only turn on brake light but not actually engage brake. Surging continued. Have tested in first, second and third gear and chugging continues in every gear. Car does not shift up to OD while rpm's are fluctuating.
Horrible fuel mileage. Around fourteen to fifteen mpg all highway miles. Have not really noticed raw fuel smell. Seems to idle fine. In Park or Neutral you can hit the throttle and cannot hear a miss or sputter whether you ease into the throttle or hit it hard. Fault code is not always thrown. Check engine did start flashing today right between 1500-1800 rpm's as I was trying to accelerate out of chugging. It quit flashing but stayed on. Code came back as P0300 again. The check engine light will stay on but will clear itself after a few days.
Have thought about replacing the spider injector assembly with the new upgraded injector assembly. But concerned that is not the fix as it runs fine after it gets up to operating temperature and is shut off and restarted.