02 4.6 4x4 manual. i have larger than stock tires no lift. it does it in every gear except 1st. if i shift up to the next gear and my rpms are below 2000 the truck seems to misfire. it stumbles and jerks. still does it up past 2000 but not as much. doesn't do it every time but most of the time. i have already changed the spark plugs. is it just because i have larger tires? am i just shifting too early? not sure and dont really want to pay the dealer to tell me there is nothing wrong.

 

did you use dielectric grease inside the cop boots? whats the mileage? and what kind of plugs did you use?

 

80000 yes i did. it did it before i changed the plugs

 

Get a new set of cops from Global on Ebay (about 90 bucks) and change them. While you are at it, if you used anything but Motorcraft plugs, change them too.