All tight and in place.
That's usually a hardware problem. Check if every hardware and connectors are tight in it's place. Try using only one ram stick at a time and check if it lags again. If it does check again using only the other one.
Remove your gpu and install it again well. If problem persists then try switching your gpu with a friend's gpu which has no problem.
if you find same results then try replacing your ssd with a sata or from a friend's ssd for a while.
I think rather than ram or gpu or ssd or sata everything is fine. Let's hope there's not any problem with your motherboard slots.
Cpu is fine or else pc won't boot up.