97 Jimmy4.3 rough idle

I have a 1997 GMC Jimmy with 4.3. The service engine light came and and I took it to Autozone for them to read the code. The code read as P300 (Random muyiple cylinder misfire). The code was reset and has not reappeared, however the idle is very rough. The vehicle was tuned approximately 3 months ago with new Delco plugs, cap, rotor, wires, fuel filter and ignition coil. I am at a loss as to what may be causing this code. The vehicle has 123,000 miles on it. The 02 sensors have not been replaced ( a mechanic advised this would not cause the code or a rought idle). Is it possible for a fuel regulator to leak and cause this. We have had some hard starting for the past month where you would have to turn the vehicle over two to three times before it would run. I should also note the fuel pump pressure was checked and it was find.

Any help would greatly be appreciated.

is this the Vortec 4.3 Wseries?
If yes this engine is know to have fuel pressure regulator problems...?