I found the exact same frustration. To investigate further, I played around with the MDL files for some favourite trains (for me mainly the DualStoxx), adjusting power, tractive effort, weight and top speed in various combinations. What I have found is that if you make a train faster, lighter, more powerful, etc, you get some amazing performance in some places but then it screws up in other places. No matter what combinations I try from moderate “improvements” to extreme ones (e.g. insane power/tractive effort, lower weight and a top speed of 300km/h) the averaged results on any given journey do not beat the original vanilla settings. If I wanted to be kind to the TF developers I would say that they probably put in some kind of “physics” algorithm to prevent people modding trains in stupid ways that made the game totally unrealistic. On the other hand, maybe it is just broken… thoughts, anyone?