Yes time to replace...
NGK's just did mine, runs great
NGK and Denso are both OEM... make sure you have a few wrench extensions on hand, a swivel might help too...
I have used NGK since the first change at 30k (now at 150k) and they are great. But I would use Denso interchangeably. The thing is I live two miles from a NAPA and 15 traffic choked miles from a dealer. So I use NGK from NAPA in everything except my 1966 IH tractor and the air-cooled engines (still on Champions).
Those plugs have more wear than I would expect, but I'd run them the full 30k if there are no problems. 13k is really short for plug life. How is the gap?
Just replaced all 6 with NGK. I think it is easier to replace the driver side than the passenger side.
Pictures is what came out. Wire brush is the "radiator". See the difference between the plugs in the 1st and the 2nd pistons (near the wire brush) to the rest. The grounding metal has a different shape.
The pictures I posted earlier is the same plug No 2 closest to the battery.
Denso and NGK are just fine. Keep it dual spark and you will have a happy truck. Although, I do agree that 13k is a bit early for replacement. doesn't hurt to change them though for peace of mind.
Toyota has put a spark plug in the newer 4runners. i dont know what its called but it has three prongs that come up into a circle. they are like $11 per plug, thats what the PO had put in mine and they are fantastic. they have a 100k warranty on them
I know i called BS on it too but i called the dealership and they told me everything i wanted to know about them. they have been in mine for 35k and they are still looking and performing amazing.