Lapres_3 || Had this very issue with my Cobalt SS. Turned out to be dirt-water getting into the ABS connector on the front passenger wheel hub. The little built in rubber gasket in the connector receded and allowed some crud to get into the connector. I took it apart and cleaned it, then repositioned the boot to seal better. Its a quick (low tech) check that can save some headaches... If you find dirt in a connector its probably the culprit even if the failure is intermittent... Pay attention when pulling the connectors off, if it feels gritty and scratchy then it probably has crap in it, regardless if you can see it or not.
I have also had experience with an intermittent ABS problem with an 06 Equinox. The stealership could not properly diagnose the problem so they suggested the sensor be changed for a meager $450.00. I bought the part and fixed it myself for about $138.00. After replacing the ABS right front sensor....the problem still persisted. Long story short.....it was a connector with crud in it. Cleaned out the dirt.........fixed!
Save yourself some money and do as Lapres 3 suggests. This seems to be a GM issue not just the GTO.