Sounds like you have other things running that are causing your issues. A gt 1030 can max out gta 5. Your cpu seems beefy enough for it too unless a meltdown/spectre update gimped that.
Try using ram cleaning software. Sometimes you're only using 3-4GB but some programs or Windows sucks out 50-100% of their performance, slowing down everything else. Personally I use Razer Cortex and disable the other Boost options. Otherwise just look up any program/utility that does that.
