Your post brings up an intetesting point. If EMD, GE and ALCO load differently, did that cause the units from different makers to buck each other with throttle changes?
Yes, when starting. That's why a little bit of locomotive air brake is used when initiating movement. It smooths out any fighting among locomotive units, and, of course, enables very gentle stretching of slack in the train, if the locomotive is coupled to cars.
Once the consist is moving and all are loading, the locomotive couplers are stretched tight and there is no more bucking, in spite of different loading characteristics or methods of making transition. Unless -- there's always that one exception -- the front locomotive is an Alco, in which case, when that unit makes transition, its whole world drops out and then the unit rapidly loads up again at higher amperage. The whole thing only takes about two seconds, but creates a bit of slack adjustment between the first and second unit. Nothing severe, but definitely noticeable. Fortunately, differences in wheel size due to wheel wear prevent all Alcos from making their speed-driven transition at exactly the same moment. On very -- I mean very -- rare occasions, and strictly by coincidence, a solid consist of Alcos with identical wheel sizes was created, and then the whole consist bucked during transition. Extremely uncommon, but it has happened.