Yes the stuttering can be due to background apps running and using up resources such as CPU load and RAM.
Yes your hardware surrounding the GPU is pulling it through, making it seem like the GPU isn't as old as it is.
Yes, even if you have a Nvidia TITANX GPU but you have slow mobo, slow ram, old HDD, and a sluggish CPU then the GPU no matter how good will be hindered in performance. This effect is known as "bottle-necking". Like the neck of a glass beer bottle, the speed and flow volume are reduced at the neck due to compressing the fluid into smaller room for travel.