1997 s10 abs brake problem

I have a 1997 s10 ext. cab pickup (vin x) with a 4.3. I started getting an ABS light when I start up the truck. It usually goes away after I've been running down the road a few minutes later. Sometimes when I'm stopping my brake peddle gets hard and you can feel and hear this buzzing noise coming from the braking system. When the peddle gets hard the truck does want to stop properly. I can pump the peddle a couple of times and the peddle is normal again and the truck stops as it should. I sometimes get a light when this happens but not always. I've checked the brakes and changed out the front pads. I've cleaned the front prox pick ups and cleaned the rotor slots (cogs). Any body got good answers or is this something I need to take to a mechanic so I wont be just part swapping? thanks

You need to pull abs brake codes when the light is on befoe you turn key off.
Post back code no.
MT