Just changed the oil in the truck and while in the air, greased the driveshaft and u joints. "Clunk" has disappeared so far. Here's my theory: when the truck was previously serviced by Toyota for regular maintenance, they most likely had the truck on a drive on oil change hoist - ramp type. If they lubed the driveshaft while on this hoist, the driveshaft was not fully extended. Having the truck in the air with the suspension hanging down may have allowed grease to enter areas where it didn't go before.

Just a theory, hope the fix lasts 'til next oil change