Soft scrub or Tilex (both have bleach) or Simple Green/Bon Ami and a scrub brush and much more work than I'm capable of anymore have helped me in the past with your type of dirt.
I have seen people destroy gel coat with pressure washers when too strong and too close.
I think since you've done all that work you really deserve to HIRE a local detailer to put a crew to work for a day.
