So I went to a new mechanic and when I got a tune-up recently he installed 5mm sparkplug wire on my 96 Taco. I normally see thicker like 8.5mm wire. Is that okay? or was he trying to cut costs?

 

probably just fine since it comes from the factory with wires that small

 

I think the small wires are correct for your truck. My 99 4runner has the thinner wires and I've read on here that the "factory" wires must be used. He probally knew what he was doing. It would be resonable to ask him if he used the smaller wires intentionally.