my 2004 f150 super crew 5.4 has had the spark plugs and wires changed in the past year and the 5th coil pac changed as well. It is misfiring terribly at around 1700-2300 rpms especially up hills and when towing. the check engine light is on and sometimes blinks as its misfiring. My mechanic says its the cam phasers but those are expensive so i am trying to find a cheaper problem that would cause it to do this. its gas milage is around 13 mpg right now which could be a result of the problem.any help?

 

Plugs and/or coils.

Read out the OBD2 codes and post them.

 

What brand plugs?
What brand coils?