02 mits montero sport engine missing
 

I have changed plugs, wires, and the gasket for the plenum. I also changed the ignition coils and no change. Its the 3.0ltr V-6 with 86k miles, the engine feels like its missing and the check engine light came on so I took it to pep-boys to have the code read. They told me that it was multi cylinder miss fire. The guy said to start with plugs and wires. So I did, it helped for about 25 miles then back to the missing feeling. So I changed the ignition coils and still nothing. Im stumped!!! Any help or some direction would be great.