Question gpu usage never consistent

[ac468]

i had been noticing stuttering in a few games. msi afterburner shows the gpu usage spike at 100% then drop randomly to around 40%. this thread shows the exact problem i am experiencing but my power supply should be more than adequate for my system. i have most of the bench marking programs that popular youtubers use in their benchmarks but i dont know how to interpret the data to find out what the problem is. temps on cpu and gpu rarely reach 70

ryzen 5 2600 (stock settings, cooler)
rx580 8gb
16gb 3000 ram
evga g3 650watt psu
x2 860 evo ssd
4 120mm case fans

 

[rgd1101]

cpu temp and usage?
fresh os install?
what game? what resolution?
ram/sdd usage during the game?

 

[ac468]

Assassins creed origins benchmark 1080P MEDIUM

cpu between 50-65 usage temp:55
gpu usage randomly drops to as low as 38. all over the place temp 61
8gb ram used