Over the last several months I purchased (new) the following six Lionel FM Trainmasters:

Virginian 6-8950
Southern Pacific 6-8951
Chicago & North Western 6-8056
Santa Fe 6-8157
Jersey Central 6-8687
Southern 6-18301

  The first three I purchased (the early versions) ran just fine in both directions, no problems. However, with the Santa Fe and Jersey Central FM I’m experiencing problems with one of the train’s trucks de-railing at random areas of track (not at the switches by the way) for no apparent reason. Sometimes it might be the forward truck, sometimes the rear and direction doesn’t seem to make a difference, at some point a truck will de-rail.
  Just FYI, I am running on Super-O track powered by a (275 watt) ZW transformer. I have several Lionel post war engines that run all day long with no issue. I have inspected the entire track for possible causes such as connection, rail mismatch, etc. but can find nothing apparent that could cause these derailments.
  I have also ‘bench tested’ these FM’s (off track) but they seem to run as expected. My only guess as to these derailments is that for some reason one truck loses power or possibly tries to change direction. Since this derailment happens very suddenly, cutting off all power it’s impossible to tell just what’s happening at that moment …it’s driving me CRAZY!!!
  Can someone please help me with this problem or offer some constructive advice as to how I can correct this?

Thanks in advance!