First thing to try is to ensure that you have the most recent drivers for the GT 730.
Download the latest official GeForce drivers to enhance your PC gaming experience and run apps faster.
www.nvidia.com
Then, try setting all of the graphics options to their lowest settings in GTA5. This might get rid of the issues you're seeing. If it does, increase the settings one level at a time, until the issues result - the level below this is what you will have to use.
However, if changing the graphics options doesn't change anything, and you still have lines and scales on the screen, then the next thing to do is to try and provide some extra air flow over the graphics card - it might be that the card is overheating.
You can do this by either adding a fan near the card or removing a side panel from the PC case to see if this helps - the fact that you only get this problem after so many minutes does suggest that heat could be an issue, although memory chip failure is more likely.
If absolutely none of this makes any difference, then you have 3 final options: ignore the problem, don't play GTA5, or replace the graphics card.