I have had few problems with this truck until now.it has the 4.6 engine and is 2WD.I started having issues with codes being thrown which indicated that the plugs or wires were faulty.I replaced all the wires,cleared the codes and the engine runs a lot better. no codes and today it passed the state emissions test.However it runs like it has a bad vacum leak and I have checked all over and can't locate one.I used WD40 and sprayed around all the vacum hoses and the intake.The engine has a miss and up to 30MPH seems to lug.The engine has 196000 miles.Any ideas or thoughts?

 

You said you changed the plug wires, but nothing about the plugs. Sounds like a plug or cylinder issue. Check your plugs. Did you use Motorcrafts if you changed them? If not, what did you use?