Not to ressurect an old thread but I concur with everyone above. I've used slippery and deep snow/sand modes in snowstorms before and it definitely helps with reducing wheel slip while accelerating. Looking at the AWD display it shows that while accelerating the power is balanced between front and rear axles. No rear axle bias like in sport or normal. Slippery also seems to skip 1st gear and starts in 2nd from a stop, as the higher torque in 1st can cause wheel slip. I'm not sure if it does that in deep snow/sand mode. I believe trail changes shift points for more torque and increases engine braking from what I can tell. I would imagine it also includes the balanced power distribution among both axles but I never really checked before. I don't use it that often.
I always wondered if eco mode deactivates cylinders. It seems to me that it's plausible, but I haven't found any documentation stating that. Definitely the noticeable part is the shift point changes along with throttle response modifications. Even while cruising in 10th at higher speeds there's a noticeable difference in throttle response. Honestly I don't see that much of a difference in fuel economy, especially at highway speeds, maybe 1 or 2 mpg (I average about 20mpg in daily driving). I could see how possibly in more urban stop-and-go environments it may be more useful as it changes accelerating patterns significantly.
I'm certainly no expert in this but these have been my observations over the last year with my ST.
Cheers
