GTS, one of the REI cars

What type of rear diff was used in these cars? (Tex Racing tags on it with fluid cooler) I have the trans out for some work and was looking at the rear end. I was wondering if it is either an open diff or just wore out. If I turn the drive shaft by hand I can stop either wheel and the other turns freely and if I hold the drive shaft still and turn one of the wheels the other turns in the opposite direction. Thanks

It should have a true trac.