Indeed the "43" file is there along with the latest DX10 &11 stuff. However, I share the stuttering problem. My FPs is typically in th 40 to 50 range traveling the route. However, when Trainz loads a set of textures for the next radius from the train's position it can drop to 5fps and the screen can freeze for over a second. In my view, dulled with age, Trainz can grab a lot of items in some routes as it tries to stay ahead of the train. It seems to be VERY inefficient in either its choice of API or its method of applying the items to memory. It may actually store them in its own memory queue and later transfer them to the GPU. Somewhere in that chain it stinks.
If you use a route that does not have lots of items where the assets are ONLY for context then stuttering is probably not evident. A desert route might be an example. Trainz can quickly determine that it does not need to grab more sagebrush since it already has it in its memory queue. However, on an Eastern route with lots of trees, crossings, towns, industries and casual villages the visual demands can be quite heavy and the pre-loads of future stuff a drag on the system drying up the feed to the GPU. I dislike deserts (real ones) so I stay in the East. I prefer a rolling hills route so I am not plagued with lots of vegetation on the surrounding hillsides. Farms with ground textured fields look good and have little impact. The upcoming Evansville route from Dremmy looks ideal to avoid stuttering.
Intel i2500 3.3ghz, 8gb, GTX550 1gb, W7-64bit