FlaSteve

Hello All.
My South Florida, concrete, three car driveway, is now twenty five years old, and looks it.   After all the twice a year cleaning, the concrete is somewhat pitted.  My usual session is no longer removing, what I guess to be, a build up of dirt and grime in the pits.  I have only used my rig (DeWalt 4200 psi, 4 gpm pressure washer, and AP+ 21" surface washer) to this point.  I never got in to pretreating, or using detergent.  That's due to the various, and often conflicting recommendations, that I've read each time I've researched.  I never came to a workable conclusion in my mind.
I'd greatly appreciate a coherent solution, from a knowledgeable person, if you have the time, and thanks in advance.  I'd like to read a  full description of what I should do at this point.  Specific equipment.  Detergents and pretreatments.  And method and technique.  I'f needed I'll purchase a downstream injector and the like. 
Cleaning twice a year is enough, the last cleaning stayed just four months.
Thanks,
Steve