So the Th400 in my K30 is an HD model, says the PO. I believe him because the guy is a gear head, and said he had a heck of a time finding a complete new trans for the truck when the old one blew, and thought he remembered there being something different with the gears. Sounds like a 475 to me that has strait cut planetaries in it, as I can also hear a slight "gear" whine when I take off. Is that what an "HD" 400 is? Let me know what you think.