I have two issues not sure if they're related or separate, p0300 code random/multiple misfire and when pressing brake and turning steering wheel car wants to die. So far I have changed all spark plugs, spark plug wires, rotor and cap, ignition control module, ignition coil, map sensor, fuel pump, brake booster, tension pulley, serpentine belt, and master cylinder (the last five were for separate issues). After replacing everything I still have a rough idle, car visibly shakes from misfire, poor fuel mileage, when turning especially when foot is on brake car wants to die. I'm not sure what to do next any ideas are appreciated.

 

Which motor in it?
Engine to frame grounds good? Try adding an engine to battery ground.
Plug off brake booster vacuum and see if it wants to die with it disconnected. Just because booster is new doesn't mean it's good.