I've decided the derailing issue is the MTH Realtrax joints do not line up well and the funky way the trailing truck mounts. The truck ends up a but cockeyed allowing the edge of the wheel to dig into the poor track joint. I experimented with a piece of thin card stock to keep the forward part of the truck from sliding too far each direction. I now have about 40 minutes of run time without derailing, although the same two cars as noted above uncoupled once more during that time. Getting better all the time.
Steve
