Is that something that just started happening with the latest release or was that happening before?
It really should be smooth even at high speed especially if velocity isn’t changing. Do you see the same issues if you just slap smooth sync on to a vehicle in one of the vehicle templates? You can smooth things out more by setting the position lerp speed to a lower value but that will also mean your vehicles will be further behind their actual position. You can also try increasing interpolation back time to avoid extrapolation. Extrapolation can be less accurate so I could see that contributing to non-smoothness. That will also put your vehicles further in the past though.