Engine runs fine but seems to seize after wot

After rereading the original post, and seeing "same thing happens in park", I came to the conclusion that my theory is likely way off; which is why I couldnt finish it.
-So, in park,all the circuit pressures in the trans are dumped by the manual valve, and even if the TC was all locked up, it would just become a very heavy flywheel.
-Assuming the engine really is seizing,that takes us back to; rings, pistons or main bearings. That means proving it by attempting to manually rotate the crankshaft, sparkplugs out, with a bar/socket on the dampner nut. If the bearings are seized the crank will not budge, but if its pistons it may move a tiny bit, back and forth. If its end gaps butted there may be a bit more crank-rock.
-In any case the only remedy seems to be engine tear-down.
-There is another scenario; hydro-loc.But the OP doesnt mention coolant loss, or coolant in oil,or steam clouds. And a 3 hr cool down period is likely not enough time for the coolant to drain away sufficiently enough to restart "like normal".
-So I guess I will have to concur with the previous poster(s) who said endgaps; even though the OP says he is tired of tearing the engine apart, as I cant imagine the damage not having been obvious enough to change the assembly specs. -Well, I guess there is one other possibility, however improbable; insufficient piston to head clearance.
-How-some-ever; in the event that the engine will turn over with the bar/socket test, proving that it is not really seized, then I would lean towards an electrical issue.