Engine runs fine but seems to seize after wot

-Ok,now we are getting somewhere.
-So heres the recap: Under Wot condition, in any gear including Park, at up to 5000rpm, engine QUITS to 0rpm in 1 second. Then attempting a restart, engine cranks very slowly, like battery is dying, but wont fire up. And it will do this also while cruising at say 30mph in Drive,going wot.Then 3 hours later cranks and fires up as normal.Oil pressure and coolant temps are normal.
-And it never; bogs, hesitates, sputters, or gives any sign of distress. It just stops running.
-That sound about right?
-And youve had the engine apart (several times?) looking for the problem and found nothing?And it still doesnt burn oil?
-Have you tried it with open headers or at least without mufflers, to prove its not the exhaust system? Does the engine seem to be making good torque under non-wot conditions.You know what, if somehow the exhaust backed up I suppose it could overheat the rings and/or pistons,maybe to the point of soft-seizing.I have seen that on small one-cylinder engines. But 5000 rpm to zero in 1 second.....I dunno.Seems like a longshot.
-Ok thats it for now. Ill keep watching.