Someone else answered me and said that with the electric operator disconnected,
and the door half way up, make sure that the door sits level---It does. Another
answer said that the tracks have to be parallel with each other---They are. From
the bottom, all the way to the other end, there is no more than 1/8" difference
left to right. This has me totally baffled.

Merely parallel to each other isn't good enough. They also have to
be vertical, and centered, and parallel to the cables. Move the cable
that's pulling on the binding side of the door about 4" closer to the
center.

I don't suppose you'd consider posting a picture of the offending
door, tracks and hoist somewhere?