speccy not showing the right amount of physical memory of the GPU

hi,

i have the GTX 870 6GB.

but speccy shows only 2gb for physical and 2gb for virtual memory.

but my GPU has 6gb of ram as you can confirm here: http://prntscr.com/q9lw4h

for some reason, the dxdiag also shows that i have 2 GB of GPU physical ram.

task manager shows me something different and nvidia control pannel shows me also something different.

i got a bit confused already :(. can smb help me please.

thanks

speccy.png