That RAM should be pretty decent. But, checking system requirements, I do see Rust wants 16GB RAM, so yeah, that is probably the issue with Rust at least, but GTA 5 should run on 8GB. Patches and add-ons can increase requirements though, so you could very well be correct on it being your RAM. I didn't realize Rust had such steep requirements when I answered initially. You can get a couple of 8GB sticks for about 145.00 on Amazon or you can get 2 X 4GB sticks or a single 8GB for 65.00 to 90.00, the brand being the only real difference. If you have a single 8GB stick, I would get a second. If you have 2 X 4GB sticks, do that. You want to try and match what you have somewhat. Matching RAM isn't a critical issue like it used to be, but still, you do want to try and at least match the individual stick specs if you can in terms of speed.