Nvidia GTX 580

Hello. There is a problem with Nvidia GTX 580 3GB from HP test program Furmark, initially shows the FPS value is 60, then when the temperature rises to 64-65 degrees, the FPS drops to 30. The decrease of the above values is accompanied by decrease of loading of video memory (see attached file).

System configuration:
Windows 7 x64 Professional
AMD phenom II X4 965 BE (acceleration to 3752)
Zotac GTX 580 3GB
Asus 970 Pro Gaming/Aura (2 PCI, 2 PCI-E x1, 2 PCI-E x16, 4 DDR3 DIMM, Audio, Gigabit LAN)
Kingston HyperX KHX1600C10D3/8G
Kingston HyperX KHX1600C10D3/8G
OCZ-VERT EX3 SATA Disk Device (SATA-III)
Sistemnaja the Asus 970 Pro Gaming/Aura (2 PCI, 2 PCI-E x1, 2 PCI-E x16, 4 DDR3 DIMM, Audio, Gigabit LAN
The cooling of the processor 240 Capitan
Graphics card cooling - water (custom), the waterblock just for the GPU, the cooler is operating normally.