Stripper.

I also heard the gom'ment took the good stuff out of stripper this year. I don't know. But do this, use aircraft stripper hopefully, it is the strongest. Put it on heavy, put a piece of plastic over it and keep it wet as long as you can, Use a putty knife to scrape, and go back and do it again where it left paint/primer. The original primer/paint as pretty tough!! Be sure to get the stuff out of cracks and everywhere, otherwise you will have big trouble when the prime.