Hi MrTatoad, well about the collisions in 3D, I use another mode, just because the game in view in only camera position.
I make the 3d Collisions whit 2D Sprites, I put an Sprite in the same pos of the 3D object, and whit a similar measure, and make a simple 2d collision whit Box or Pixel Perfect Collision.
I don´t stay very sure, but I think it´s more speedest for calculate, than a real 3D collision, how I say I don´t be sure about this, but I think by logic a 2D collision needs less calculation than 3d, no?¿.
This it´s only for a fixed camera, but if can be made work whit animated camera, ok, needs a little more work.
Perhaps the trouble whit the 3B object it´s something about the expoter of AC3d, I go to try something whit 3ds MAX, and I tell you here!!!

Kinds regard,