Running Rich

Have a 2002 F-150 Lighting Series 4.2 liter 6 cylinder 5 speed - It began bogging down and stalling - took it to run OMD and it's running rich...
Changed the fuel filter still having the same problem
Any suggestions on what it could be or how to fix it???

Check the air filter and air intake, just in case its blocked, has a dead rat in there, etc.

Scan the ECM for codes. Post back here with your findings if you like.

Assuming it runs okay with no obvious misfires, I would suspect the oxygen sensor first, but there may be other issues.