Rich,
Here is what may be happening if you do not have Ross Ready switches (pre-wired). If you have Ross Ready, ignore. On Ross Ready switches, all these rails are connected to other rails with power (probably).
The area of the yellow arc has no power for the front truck, so only the rear truck would be getting power. If for some reason you are not showing voltage (volt meter) between the center and outside rail your train will stall.
You stated you have already checked this, but just a reminder that the whole center rail between the switches would need a power drop since they are not connected to anything.
Again, all this is only if your switches are not fully Ross Ready.
