i am hearing a popping under the pass side of my truck any idea what it could be. its random and happens every 15 20 miles when cruising on the highway. the truck is an 02 sierra 1500 (sorry it not a diesel) 4.8 with 210000 miles. thanks

 

Ball joints, torsion bar seat and the list goes on and on.
Best place to start is jack up driver side and look for loose or worn parts.
Honestly, To save your self some time run it by a local shop and they'll have you diagnosed in no time. Professional shops are equipped to diagnose and repair much faster and most likely cheaper than it would be for you to attempt on your own. Not being mean, just calling it as i see it.

 

ok thanks but why would it be at highway speeds

 

It could honestly be anything bud, Without hearing it, its about impossible to diagnose.
Heck its virtually impossible to correctly diagnose on the computer anyway, Kinda like a tech listening to your vehicle and saying yep, i know what that is.... You dont know what it is until it's fixed from my experience