Wanted to give an update after a little more testing.
Saw someone elsewhere suggest disabling DLSS (and avoiding all other Upscaling options as well) and the large frame time spikes and severe stutters dropped off for the most part (still around 5-10 total during a stage), but there were still smaller stutters and microstutters happening a lot of the time instead.
On the frame time graph it went from this constantly (using DLSS): 
to this (No Upscaling): 
and this (No Upscaling) : 
Even these minor frame time spikes / microstutters are still enough to interfere with your driving, and Gsync doesn't smooth out these hitches showing this is more than just minor framerate variations and performance drops but rather some technical hitch, although it's not nearly as brutal as before.
I don't know if the upscaling methods in game are currently busted or if they are just exacerbating the underlying stuttering issue making them more obvious when they occur, but yeah.
I know this tip won't help console users, but if you are playing on PC, give it a shot. It went from unplayable to nearly playable here.
