First off you won't get FLAT with a DA on a HOOD!
You need to long board. If it's just a skim coat, then long board with 80 grit.
Yeah may be time consuming but flat is time consuming.
Once you think it's flat. Shoot it with 2k primer. Shoot a guide coat on it and then again long board it with 120 grit. Watch what your guide coat is telling you. Are you low in any areas? High because you show metal?