Code P0300...how to troubleshoot?

I have a 97 1/2 Regal GS went to my friends shop to use OBD....it pulled code P0300. This code states random engine misfire. Under further testing OBD stated cyl 3 misfired about 400 times, cyl 4 misfired about 200 times and cyl 5 misfired 1 time... Car had new plugs, wires,fuel filter,PCV,air filter, and Techron injector cleaner put in about 10,000 miles ago...now the car has 115,000 miles on it. OBD suggested it could be O2 sensor, coil pack, EGR, fuel injectors and i think even the cat... The SES light never came on....the motor seems to run fine.........I did put a tank of gas in and the car seemed to run crappy for a while....any suggestions would be appreciated...I know if a cylinder misfires 400 times is a really low number....the code was reset and test drove for 10 miles and re-tested and pulled no code...am i looking at a future problem?

This sounds like an injector issue. I would have the shop professionally clean the injectors and see what happens. Due to the fact that the misfires are random and not tied to any one specific item like a coil then the injectors are probably either getting dirty or are failing. A professional cleaning works much better than the in tank products and should take care of the issue.

No codes after reset? Drive it for awhile and rescan. Codes were probably just stored in there.

I agree with Rip, if the car isn't showing any more misfires since the clear, some of those mis-fires could be pretty old indicating no problem exists

Also, try dumping a can of C-foam in you gas tank. You can get that at any automotive store and it works wonders. Just make sure you use 1 can to a full tank of gas. That will literly clean the shit out of your injectors.