Brake Problems!!!

I'm having problems with my brakes. For the last 3 days, the ABS light on the dash comes on and stays permanently on after driving for a few miles. Sometimes it will go off momentarily and then come right back on. (Note that when I crank the truck up the ABS light comes on as the system goes through it's usual self diagnosis check and then goes off after a couple of seconds, which is normal) Well yesterday, I noticed an unusual vibration/noise comoing from somewhere within the truck but didn't give it much thought. When I got to a red light and hit the brakes to slow down, the brake pedal felt unusual. It seemed to not want to move past a certain point and at the same time I could feel the ABS pulses. Anyway, at the next stop light, the same thing happened but this time the truck started pulling on to one side and I actually had to dial in some counter steer to keep the truck straight! This freaked me out big time. Funny thing is that as I pulled over to a nearby parking lot, everything seemed to go back to normal except the ABS warning light on the dash remained on. Can somebody please clue me in on what's going on with my truck?

What year truck? Is light staying on constant, binking a code, or just blinking erratically fron time to time with ni rythem?

Sounds Like You May Have A Vehicle Or Wheel Speed Sensor That Going Out. May Also Have A Caliper That Is Sticking