Before trade a new CPU and mobo, I would contain tried the less classy ideas (RAM, or GPU). You could have a terrible memory stick; although doubtful because you did test each one separately but still a slight option. You say when you place in an older PCI card rather than you’re PCI-E it ran much longer, were there any other suggestions? Did you check GPU and CPU temps? What are your system voltages and are they in sync with manufacture specifications? If you have a different PCI-E card, perhaps give it a shot.