I would agree w/Stig's FIL about the truck...
My F150 got 160k miles on 3 plug changes and maybe 4 or 5 oil changes ?
Just began the third set of tires, and it spent most of it's life with a mid sized load of construction materials and tools.
Worked fine until I got clobbered while on the hi-way... T-boned, driver's door !
A defective coil pack, or wimpy fuel pump causing a miss under heavy load was the only performance problem I ever had.
Fresh plugs never did fix the stumble it had, from time to time...
redk