Special k frame limiter on with vsync on = stuttering

my gpu is nvidia card currently

before, when i use radeon gpu there was no problem

but after swapped to nvidia card with vsync on

everytime framerate drops below refresh rate, frametime spikes

but when framerate fluctuate in gsync various refresh rate (in my case it’s 48-75hz), it does not

so i usually play with vsync on, gsync on, fps caps to 73 or 74 with rivatuner

then i heard special k framerate limiter is more stable than others

so i tried but whenever framerate drops to below limited fps (73 or 74), frametime spikes

i did check almost everything with special k options eventually once i turned on nvidia black magic option (some name like this) to low latency or low latency + boost, frametime suddenly align more stable

but i want to use frame limiter only what can i do? sorry for my english