OK, more than likely, there is a broken wire going to one of the front wheel speed sensors. The "acting strange" was actually the ABS engaging. Because these wires flex everytime you turn the wheel or go over a bump, after awhile the wires inside the insulation begin to break (although the insulation remains intact, making it appear visibly sound). These breaks in the wires cause intermittant connections, which the ABS controller reads as "wheel lock-up" and engages the ABS. After some time of doing this, the breaks in the wires start to pull away, which causes the ABS controller to set a wheel speed sensor fault code, turn the light on, and disable the ABS.
Two things to keep in mind:
1) there are only two ways to know which wheel is causing the problem, and thats either use a scantool and have the ABS fault codes read, or remove the insulation from the speed sensor wiring harnesses and find the break (usually within 8 inches of the sensor connector).
2) Most shops, when they see a wheel speed fault code, automatically assume the wheel bearing (hub) is bad, since the sensor is internal to the hub. I would estimate that 3 out of 5 speed sensor codes are NOT the hub, but the wiring to the sensor, like I mentioned in the first paragraph. GM sells replacement connectors with wiring to repair this, if that is indeed the case.
Please let me know if I can be of further assistance!