My 2009 Tahoe LT, 75k miles, started running rough a few days ago. Check engine light flashing, dash reading service traction control and service stabilitrak. Computer gave code P0304, misfire in cylinder 4. So we changed the spark plugs which seemed to fix the issue, but very briefly. Again, running rough, engine light flashing and service stabilitrak. Again gave the same code. So we replaced the ignition coil in cylinder 4. Did not fix issue, computer still throwing code P0304, and now also giving code P0521- Engine Oil Pressure Sensor/Switch Range/Performance. Any ideas at what could be causing these issues?

 

Switch the coils with the one next to it and see if misfire moves with the coil swap. Aftermarket coils can be bad out of the box. Genuine GM electrical parts only for replacements.
Oil pressure switch most likely is a separate issue. They go bad or the little filter under it is plugged.
If coil swap doesn't work a compression test is in order to see if AFM lifter issues are present.