That pulley is the main tensioner for the serpentine belt, you can put a wrench on the lower pully section and see if it's too easy to move, the spring tension might be getting worn down. It does appear to be moving quite a bit, I would take the belt off and check the rest of the components that are driven by the belt. Make sure everything spins freely. Might be time to replace that tensioner and check the belt for any cracks as well. Make sure to draw out a diagram of the belt routing before removing it, that way you'll know how the new one goes on. Hope this helps.
Here are the different belt routings for your truck:
Friday, January 27th, 2023 AT 9:02 AM