What would cause a high pitched whistle under acceleration, at all speeds.

Do you have an aftermarket cone air filter/cold air kit? I've seen these things laying on the shoulder of many roads. Definitely sounds like something on the intake system.

If it only does when the truck is in motion, remove that stick that's now rubbing on the driveshaft! In other words look for something it picked up off the road when you "ran over some debris".