A lot of the time the problem is you have to use a like for like card because the heatsink for the CPU also caters for the GPU and on another card the chip might not be in the right place for the heatsink. Have you found replacement cards using that P/N?
You could always try the oven trick on your GPU as you have nothing to lose. When putting it back together consider using a copper shim with heat pads so there is efficient cooling and the shim puts more pressure on the chip to help prevent solder breaks.
Thanks for the reply. Baked it lunchtime and reapllied thermal paste. Its working for now lol