Seems to me that is a very strange way of doing things why not revamp your engineering on the Drum side using a clutch & a lock to secure the platform when traveling,- then to lower release the lock & lower -- I am no electrical engineer but it seems that you have already overloaded the electric motor subsequently burning it out & only an electrical engineer could tell you this - ( that is would an AC Motor do this consistently & what horsepower would be required to perform this task & hold the load then from your info i an presuming you reverse the direction of the motor to lower your load.

Having not seen your application but from the information you have sent i would be looking at modifying my drum & cable side
by placing a gear & mechanical lock - you could safely lift to a stopping point then lock - travel - lift & unlock then lower without to much modification.

To change to an AC motor would be very expensive & you would need an DC/AC transducer & some type of software to pulse that current to the motor changing it from DC to AC.

Let me know what you think.

An example of the Cam & lock mechanisms can be found on a simple come along / fence puller type of tool.