This is what I thought to, until I grabbed the card.This doesn't add up. If the backplate is hotter than before, that means it's pulling more heat out of the board / mem chips, and the memory should be cooler than before.
Afaik, memory junction temp shows the single hottest chip, so if one chip is making poor contact it will show high temps and throttle, even though most of the chips may be considerably cooler. I would check to make sure all the pads are compressing and making good contact.
The heatsink on top of the backplate is hot as hell now and the throttling has stopped, I will check the contact tomorrow. It's working for now