#Don't do this:

private void Update()
{
    RandomSpeed();
}

The only thing you should do during Update() regarding speeds is to check to see if the value of randomSpeed has changed, and if so, generate new values (assuming that you want the boolean to change at runtime). You do not, and should not, generate new speed values every frame.

Don't do this:

private void Update()
{
    RandomSpeed();
}

The only thing you should do during Update() regarding speeds is to check to see if the value of randomSpeed has changed, and if so, generate new values (assuming that you want the boolean to change at runtime). You do not, and should not, generate new speed values every frame.