Best way to switch out property management

[Kenny M.]

In one of our locations, we allowed the realtor to be our property manager in upstate New York.  This portfolio has grown quite a bit and it seems the current PM, a one man gang, just cannot handle the management.  He's a good guy, but doesn't seem to know when to say when.  He has about five of our properties which equates to 18 units in total.  We have five vacancies and three pending evictions with and two current evictions.  He claims it's not his fault, it's the type of clientele of low income (700 - 900) per month per unit.  He doesn't always respond to us in a timely manner, I mean days or not at all.  One unit, which is a half a block away from a college has been vacant for several months.  We've interviewed a few property management companies which have several hundred units under their management and 5 + employees.  They seem keen on taking over the portfolio.  We have an agreement, however, since vacancies are over 60 days old, we have an out on our contract.  Two of the units don't even have a PM contract yet.  

What is the best way to transfer the properties?  Should we gradually take them away?  Should we split them between both companies?  I just think the realtor/PM is overwhelmed as he's not a bad person, just doesn't have the resources to manage our properties.  He's trying, but due to the vacancies and evictions, we're losing about 4k a month.