Considering that there may be game engine changes, using the new vehicles with the previous game version may not show all the features correctly. Installing them as a DLC to the old patch won't give identical behavior to using them natively on the new patch.

Any new amphibious vehicles?

Well until ScriptHook updates it'll be a bit difficult to test add-ons since there's no way to spawn them.

Does anybody know if the APCs ever get driven by NPCs in GTA:O? Or are they only ever driven by the player? So far it appears there's no way to get an AI driver to use an amphibious vehicle without driving like a complete dumbass.

It's been 3 hours and you requested a mod that amounts to "make an entire new game". Have a little patience.

I vaguely recall seeing these once, but have been unable to locate them on any vehicle when I went to check just now.

Explosions aren't textures, they're particle effects. There is currently no way to modify ptfx.

What mod are you using anyways to spawn add-ons in traffic? Why not just edit the popcycles files to add the cars you want? Let the game engine take care of it and don't run additional scripts if you don't need to.

Far more likely that the memory leaks are due to installing shitty car mods. Fact of the matter is, add-on cars in ambient vehicle traffic isn't a good idea. Most add-on cars have no LODs, are high-poly, and are generally not suited to spawning a large quantity driven by AI. Using a trainer to spawn one add-on car shouldn't be an issue. It just creates the vehicle, and then the script is done entirely. Any issues after that are the model's fault, not the script's fault.

As FoxtrotDelta hasn't had time to do this conversion as he originally thought, I'm still looking for anybody interested in converting this model.