Greg:
First, do not get discouraged by anyone, someone else is doing it so you can, not going to be easy.
If not done already I suggest to look into this:
Enforce that PM uses a great website for rental screening, ones with a background check and choose the best tenants possible.
Review you leases to close any pitfalls and enforce the lease to the T.
Keep the units in good shape and keep extra cash reserves ( fixing + trip expenses )
Tiger than normal lookup on the PM ( have second PM line up ), vacancies, unit showing costs, repairs, fees, etc, require a once a week normal operations report and a once a month full operations report.
Family, friend on virtual assistant that regularly drive by the property and reports to you, or if cash flow allows and deem beneficial you can install security cameras and remote view activity on the property, nowadays there are lots of options.
Check if feasible to get a home warranty plan for the units so some pain issues are self-managed by the tenant via a phone call to the warranting company
In which city/state is the property?
Best of luck.
RP.