You may have an issue, but it is unlikely the motherboard itself. The gaming 5 is a very good board. I can't recommend buying a new Z97 board because the prices have went way up. If you really want one though, an Asus Z97-A used to be the go-to Asus board. Not sure they are sold anymore though. Then you have the issue of buying a new copy of Windows.
Are you having issues with any other programs or games?
If we had more information we might be able to help you. I prefer 3dmark (firestrike or timespy) as it gives a lot of information at a glance. You can also check to make sure your RAM is running in dual-channel mode and your graphics card has sufficient airflow. What does your GPU usage graphs look like when playing GTA 4 (can use GPU-z for this)?
There is also http://www.userbenchmark.com/ it shows a decent amount of info as well as any major bottlenecks. Don't spam this one though as the storage test is very demanding and may cause your SSD to overheat and throttle on successive runs.
For what it is worth, it may be a case of your card is too good for the game. Not enough load on it to keep it at high clocks. I experienced this with X3: Albion Prelude. I used to have a terrible PC and it was difficult to run that game. Now I have a beast PC and was shocked to see the game stutter and get low FPS for seemingly no reason. When I checked into it more closely, turns out the GPU (GTX 1070) wasn't even getting out of the idle state.
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