I'm with Randy, don't mix brands, ever. In my years as a paint rep there is one thing that I saw, over and over, I learned, follow the tech sheets and you will by the odds end up with a better end result, PERIOD .
Just simply follow the tech sheets, M-S tech sheets aren't going to say use Dupont clear, that is a given. Just follow the sheets.
I don't understand what happened on your horizontal surfaces. Please explain.