1993 Suburban Poor Braking on Icy Roads

And you thought i was finished with the questions. In the winter on icy roads i have a heck of a time getting this thing to stop. Going under 10 MPH i have difficulty getting the thing to stop, almost causing an accident, which is unacceptable even on icy roads. When i hit the brakes, the infamous ABS sound is heard, but the car just slides. The brakes feel like they are just locking up even though they are ABS? Pumping the brakes helps stop me better than keeping a firm pressure on the pedal as GM suggests for ABS brakes. Any one else have this trouble? Thanks!