Yeah that's pretty much where we're at . The valvetrain (for lack of a definitive source) noise is persistent and gets worse as it warms up to the point that it is present straight off the idle (about 500-750 rpms). It does have your typical lifter click for maybe a second and a half after a cold start, but that will cease and give way to the noise in the video from then on. You can barely see in the vid that my oil gauge was reading about 40psi, and it does indeed work correctly

That deeper noise has (seemingly) migrated to to the driver's side bank (err, by that I mean the right one, usdm and all) in the week since the truck started last. I will replace the motor mounts before I tear it down to see if I'm getting a slight oil pan contact with the front axle, although as the video shows it is present even when the truck is stopped. My next step from there is the old screwdriver test for bad rod bearings and/or wrist pins.

As for the tranny mount, it's solid and was inspected after the noise occurred. The rubber isolator is quite flexible, but clearly not ripped. Even so I will try your suggestion when I have a second person available for it. I'll also unbolt the crossmember with the trans supported to ensure that the mount is good.

There is an exhaust leak from the right bank manifold to the y-pipe (old gasket), and it makes an audible noise that will also be remedied before the teardown.

Thank you for all of you time and thoughts on this, this forum is one of the best vehicle specific websites that I've encountered, and folks like you and the others who chime in are what make it so .