Pushing the game to its limits!?

I have been pushing this game as far as either a) the game or b) my pc can handle. I have a 900 block forklift and a 2800 block truck which I fool around with on my two PC's in multiverse. I can run the forklift alone at 100% with a good 40-50 frames. When I combine the 2800 block truck I have to drop to 9% (why can't I select 10% btw!?) then I can get 20-25 frames, which is fine for a video I can speed it back up in the edit. HOWEVER.... many times whichever machine I load second, the LOG blocks are glitched, many of them are either randomly missing or reduced to only a length of 2 for some reason, causing the entire machine to collapse!. It doesn't matter if I start at 100% or 5% this often happens. Sadly some of these random missing blocks can be completely hidden and I have overwritten my machines with the glitched versions and had to go back through and replace them all!. No other block is ever missing or glitched. Sometimes its 3-4 logs sometimes it's 20-30, usually down to length 2 with their ends missing. Of all the things you would think would fail when pushing the game this hard, the physics etc (which so far have been fine!) failing to load the machine intact would be the last thing you might expect! Any ideas?!

16gb ram