A friend and I built the comp about 6 years ago, 4mo ago the gfx card died and I replaced it with a Gigabyte GEFORCE GTX 650ti and then lag problems began occuring. Most noticible while playing WoW, but can also SEE whne simply browsing around on comp. Replaced internal power supply with ANTEC25 650 and still having the issue. if anyone could please help I would appreciate any input.Have you updated video drivers? Seen before where drivers that Windows associates with video cards unable to tap into the full potential of video card and so PERFORMANCE crawls and issues pop up occasionally.Specs ? ?Yes i updated the drivers.
As Patio requested, what are system specs?

I am thinking this video card uses shared memory even though it has plenty dedicated and if the system RAM count is only 2GB etc, then the system may be starving for memory causing problems. You can find your free memory by going into task manager and looking at what is available IDLE etc.A 650Ti is a powerful card for 6 year old hardware.
Does the PC simply lock for a few seconds or is it just a large drop in FPS output?