are you able to "lock" your focus ?
that is why nothing stays in focus in the first situation
and partly the second. you have to anticipate movement sometimes
sometimes there is a knob to turn that locks focus
othertimes, like with a speed graphic, there is a little lever ... once you focus+lock it
the focus shouldn't move at all
since "stuff" is moving it won't be the same anyways ( you , the subject &c )
that is why i use focus references /zones as i mentioned above.
i'd look into figuring out how to lock your focus before you give up completely
but then again, if you would rather use a MF camera or a 35mm, don't bother with the 4x5
its just a light and money trap