I have acquired one of the latest releases of the Athearn RTR HO SD60. I have found over time through owning a few RTR models that they are very picky when it comes to track. I have several other models that traverse my railroad just fine, KATO, Intermountain, etc. The problem I seem to have with this SD60 is the same I had with a SD40-2 model where the front axle likes to find a slightly rough spot and hop off the rail. Same problem with the lead axle of the rear truck. I had a repair shop that is no longer in business alleviate the problem for me but the gentleman is no longer around for me to ask what he did to the loco. Is the best answer to modifiy the middle axle of each truck so that most of the weight of the locos rides and the end axles and the middle one just floats? Any suggestions? I checked the axles on a flat surface and there doesn't appear to be any bent axles or warped trucks. It never hops off in the same spot either so that makes me even more confident that it just needs to be tuned a little. Thanks everyone for their help!