Just dropping this here in case you are still suffering from empty vehicles.
Spot of luck (perhaps). I haven't tried it out on my game yet but it sounds promising:
In the thread there is info about authors putting '--' (& possibly other invalid characters) in .xml files. This can cause problems (it was causing one ped in my dispatch.meta to have trouble spawning). If you have any comments in your dispatch.meta, try removing them
EDIT: I noticed your comment in the link above saying it didn't work for you but given the info above might be worth trying it out again. The mod has a 'DispatchGhostFix.log' that is produced in the main GTA V folder that may give you useful info also.