I know you are busy with other problems, but I want to suggest something anyways.
@Red-tagged vehicles
One possible fix for these vehicles could be to write a script that, when the crew are dead or out of the vehicle, creates a similar vehicle on an outlying island, applies fuel and damage levels to it, and set it in the same direction as the original vehicle. The script can then set the new tank in the position of the old one and delete the old tank. The script can loop slowly, wouldn't require any global variables, and is a one time use script for each vehicle. I don't think it would contribute to the lag very much, and it would solve a problem that is annoying at the least. There are two things I an unsure of though: How, if possible, to transfer the ammo levels to the new tank. And how, if possible (I don't think so), to set the damage levels to specific parts of the tank.
-Student Pilot