I have around 115k miles on my truck now. I'm thinking about adding some more performance mods to my truck. I currently have a superchip & flowmasters. I was thinking about underdrive pulleys as my next mod. Think the $150 for pulleys would be worth it on a higher mileage truck?

'98 F150 ext cab 5.4L auto 4x4

 

I think they're worthwhile on any truck. If your truck is in good working order, you plan on keeping it, and you have the $$$, I would go for it.