I had this gpu that it would only post on a 720p monitor, but when ever i plug it in to my 1080p monitor it would went black screen and reapear for a couple of seconds and went black again and when it reapear it would be moving at 1 frames per second. So do you think the problem is the vram or something eles?
I can vouch for the programs linked above.
The free versions are limited in amount of ram tested on some of them.
OCCT & Furmark have been arround a long time and will check all of Vram not claimed by windows.