In my experience the heat shield is more of a metal on metal rattle than a clicking like this sound is but it is definitely worth a look.

 

I think you have a bad u-joint, given the miles. You don't hear anything when you are sitting still, revving the motor. That pretty much eliminates anything related to the motor itself, or anything that would be vibrated by the motor. If you can run the vehicle up to 60 miles an hour, and you can hear the noise under acceleration, or while cruising, take your foot off the accelerator and see if the noise goes away.

If you have the truck parked and chocked, you can climb under it where the drive-shaft connects to the yoke of the differential, and see if there is any play in it. There should be none. You could jack up a rear wheel to get it off the ground, put the truck in neutral, and rotate the shaft to see if there are loose spots during rotation.

If that is what your issue is, the front bearing cross is as old as the rear, so plan on replacing them both.

 

Thanx @Kazoocruiser. It'll be a week or so until I can get under the truck. Ill check back in and let you know what I find.

 

So I finally got to the problem. There was a leak in the transfer case which dried out all the plates and some plastic pieces that caused the ticking. New case and the problem is solved! If you have a problem in the Santa Barbara area I highly recommend Goleta Transmission on Aero Camino. Ask for Steve. He had all the bad parts and took the time to explain what happened, how it happened, and how he fixed it. Not cheap but good work never is.

Now its time to save a little dough and level her for bigger tires and do the intake and exhaust system as I planned when I bought it. I hope nobody ever has the same problem I had. Have a good day.