This is happening when I am trying to play Evolution Championship’s Evolution Open at Froza Driver’s Cup, while I use my 2018 Dodge Demon Fast & Furios Edition Car.
The game stutters when I stay with the other cars. Once they move away from me the game starts to run a little better however, if I approach to them it slows down again as seen in the video.
Xbox or PC. If PC your settings are too high.
Xbox One S. Please help! 
There are known issues with the f&f cars on some tracks, especially if you use assisted brakes
As an example, try the Mazda on VIR…
Thanks, changing my car worked! Too bad, because I really wanted to use my 2018 Dodge Demon Fast & Furios Edition Car for this race.
Thanks for your help! 
I think I found out the same way you did, I was using the Mazda in one of the open cup races at vir, took off like normal, after first turn I could get it over ~40 and everyone was flying by.
I don’t think all f&f cars are affected, I think I did that cup using all f&f cars, but seems there were two, maybe three that I couldn’t use. If I recall, if I removed assisted braking, the issue went away, but I tend to use assisted braking. Cuz I’m old.