I noticed that I made in unclear in my original post - The rental amounts are before expenses. There are management fees, occasional payment to fix or change an appliance, HOA fees and property taxes. Vacancy is very low, I had perhaps 3 or 4 months without full occupancy in all the properties combined in the last 10 years. I always buy a property that has a tenant, preferably someone who lived there at least 2 years and they usually stay for a number of years before they leave.
As for the suggestion to do 1031 exchange for all my properties for an apartment complex. This is something I've seen people do, but I think this can not happen in the FL market because the prices are too high. This means I would have to go to a different state perhaps and I would need to find another property management company. I just feel less comfortable doing that at this time. Trading up for duplexes is something I consider low risk.