With my grandfathers railway when we had inertia problems we new it was time to thoroughly clean the track with on of those abrasive rubbers and maintain any problematic locos. It is amazing what a complete strip down can achieve! Use contact cleaner like deoxit on the contacts etc.. If all this didn't sort the problem then there was usually something wrong or not optimally setup!
I bet these guys know all about this! If anyone has never seen Winter Wunderland then they are in for one heck of a surprise! Worth a holiday in Hamburg in my opinion!