Yeah i had a simmilar problem, when i started getting into working on the truck, my parents of course bought it new and own it still, it was getting a really rough idle and lagged when you gunned it, dad said the mechanic told him they were platinum plugs, which the guy also told him would last 160000km, of course i was like, something is really wrong there, a factory vehicle with platinum plugs... i checked and it was the basic plugs, really worn away and i was seriously amazed the truck still ran. We put new ones in and it ran mint.
PS the plugs were 120 000km on them then