Let me guess, it bucked going uphill when in the 35-50mph zone only. Plugs were only a short term fix for me. Check your COPs and see if you have bad boots. I just got frustrated and bought a new set from Accel and that seems to have solved all my issues (2500 miles and counting). I have the 5.4 Triton in a 2005 F-150 4x4 Lariat. Now the only thing that bugs me are the cam phasers making that clacking sound...