@acjester91I was reading through the forums, and came across a solution! Make sure you have "advancedhookv.dll" in your main GTA V folder. I had it at one point, but it got deleted somehow. Reinstalled it from the ELS installation files, and everything worked!
I have been having this same exact problem! I have never been able to get any ELS vehicles to work. I have only just tried using it recently, so that does not mean it has been a long-term issue.