One thing that struck me was when you said your Dads handles well, and the other two cars don't. I think I would take a very close look at his installation and then yours to determine what is different between them. Why does his work well and yours do not?

I would be under all the cars with a tape measure, and would also find out how his is set up and aligned. Something is right with his and wrong with yours, and you just have to find out what that thing is.

It is going to boil down to installation, components used, alignment of components, or some faulty component.

Don