According to MoBo manual (page 1-15), the 2 sticks of RAM should be in the slots #2 and #4 if counted from the CPU side.
Shutdowns during gaming are mostly caused by 2 issues:
1. CPU/GPU overheats and to prevent any damage, system shuts down.
Are the listed temps idle temps? And if so, what are under load temps?
2. PSU fails to deliver enough power to the GPU or fails to keep smooth enough voltage for PC's operation.
Corsair RM series PSUs are mediocre quality PSUs though. What's the age of the system? 3 years? more?
If your temps are within normal range then it's most likely PSU issue. While PSU does have enough wattage, it's voltage regulation can be off for PC's operation under load. Here, replacing the PSU helps.
For new PSU, i suggest good quality unit from Seasonic, in 600W range. E.g S12II-620, M12II-620 EVO, G-650 or Focus+ 650,
pcpp: https://pcpartpicker.com/products/compare/WrNypg,nB3RsY,Tc3RsY,R7V48d/
Focus+ is the newest PSU line from Seasonic which comes with 10 years of warranty. Other listed Seasonic PSUs have 5 years of warranty.