On 2nd gen runners rear bumper there is this slot (hole) in the center. What is this for?

 

Thats to lower your spare tire. There is a rod under your rear seat that slides in there to a spot above the spare. Then you crank it to lower or raise the tire.

 

yeah i had that question too except when i got the truck the lift attachments werent there and i went to the dealership to see how much they were and needless to say i was off to the junkyard the next day

 

I would recommend lubing the hell out of the lowering mechanism at least every 6 months (it's located diagonally to the left of the slot towards the left rear tire) because when you go to use it it will be rusty and frozen and most likely raining and you won't be dressed appropriately (don't ask me how I know). And check your spare tire pressure as well.