I did it in a toaster over (because its so small). I did at about 400F I put a peice of lead free solder in with it and when the solder started to melt I let it bake for about 5 more minutes then turned off over and let cool for 15 minutes.
I have done a couple motherboards like this but in the oven. One HP DV9700 with GeForce Go 7150 and one Everex XT5000T with GeForce Go 7600. I don't see how your 375F temp worked since lead free solder melts at 380F Tyipicaly. Also to get a good flow with it on my soldering Iron I have to be at 400F. Thats why I use that temp for baking. I did rebake the GPU again last night at 400F for 15min. And still nothing. COmputer powers on and when its about to switch on the screen it shuts off not even the backlight lights up with the card installed. I really need to find a known good card. I was thinking of trying one out of a Cleveo D900 they look the same minus the SLi connector.