Yep, the GM plant is on the UP freight main. TRE is the old Rock Island, and yes, there's still some freight that moves on the line in the overnight hours when TRE isn't running.
In addition to Irving/Dallas and Fort Worth, there are a couple sidings in Euless (huge Kinder Morgan facility with tankers), the Kelly Moore paint plant in Hurst still has a spur, and there's an active branch into the Centreport Industrial Park right on the Dallas/Tarrant County line where you've got a paper packaging plant and a plastics plant that both still receive cars, and service to a dozen or so warehouses that have taken shipments at different times over the years.
BNSF has/had trackage rights on the TRE as well... used to be a coal train that came thru middle of the day, and others overnight between Fort Worth and the BNSF yard in Irving (which wyes off the TRE near downtown Irving).
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