Soldato
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I would think if it's not a Pciex slot connection problem (heat and weight) it is a damaged card as nasty as it sounds minor flexing of the card should not cause disconnects of any of the components.
Personally if I was pursuing your route I would brace the card whether it be with the original sub plate or some other method and also mount the fans to a case supported sub tray.
Even if I had to hack the cooler I may also consider leaving the original ATI fan for a bit of airflow on the card as I doubt you have much air penetration around the VRM's.
It seems to be an over-tightening issue rather than pcb flex
Still, those GT's aren't lightweight and some bracing may help.
Is it possible to mount the big Alpenfohn VRM heatsink under the MK26?
what are the VRM2 Temps on your cards ? my are really Bad
20% fan - 120° and increasing
50% fan - max 110°
100% fan - max 90°
my fans are 2x enermax cluster 140mm
You can if you do it Petey style