Somewhere in all the GE mods was the XR deal, for Extra Reliable. This was still in the Universal Series era; I recall a picture of a new Frisco ??? U - Boat with the XR lettering.
Regarding predecessors to EMD's Dash 2 line, another early model was the SD-45X, which had a big influence in the 6 - axle Dash 2 with its' HT-C truck. Though the modular electrical components were good, modifying the long - standard Flexicoil truck to orient all 3 traction motors in the same direction gave the SD-40-2 @ 3000 H.P. the same tractive effort as an earlier SD-45 with the HT truck & 3,600 H.P. Ironically this would soon spell the end for the big 20 cylinder brutes, with their greater fuel use and troublesome crankshafts.