This probably doesn't affect you, but there is a cluck that affects over a decade of S-10s and Sonomas. Bad bolt and washer on the hood hinge. Factory recall. Just takes a lock washer and the cluck goes away.
It doesn't take much to be annoying, but that clunk could be anything between 2 metal surfaces. Don't rule anything out, or anything in. If it's so random than you can't use a known pothole to recreate it while driving, its most likely not a suspension part.
The light clunk could be your transmission if it only happens from a dead stop. First gear engagement from within. Jack the truck up, lightly set the e-brake (for resistance) and drive. If the clunk is there, drivetrain. If not, suspension or something else loose.
If you're not stepping on it I highly doubt a bad motor mount. its possible, but every vehicle I've owned requires/required flexing the muscle to damage mounts. I can't imagine your Tundra is that big a POS that it flexes with hypermiling techniques.
If you can remember what you were doing--ie speed, gear, throttle, direction, location--and mimic that and not get the same results, you have a POS. If that's the case I would trade it in.
although its not overly common, its been reported that sometimes the fenders can actually come loose in some areas and start flapping at higher speeds. left to fester this can cause MAJOR body damage. just something to check