Tim - I think you may be on to something. The last time I drove the truck, I heard a ping in the transmission when I shifted into fifth gear - I imagine much like the one you describe. I didn't shift into fifth after that - just headed back to the house. I have installed a rear mount on the transmission, as suggested, but the grinding noise was still there.
Today I drained the fluid. It was very red, just like out of the bottle with not a bit of metallic color or gray color or any other sign of metal. The transmission is now out of the truck and ASAP it goes to the transmission man. While it's out, I'm also going to install a Schiefer aluminum flywheel to help things out a little.
