ABS Issues

I have recently bought a 1996 Tahoe 4x4 with a 4 inch lift, and 33x12.50x15 tires. The Tahoe has 153,000 miles on it.Since I test drove, and since I owned it the ABS light has been on.
By inspecting the vehicle, I have noticed that it has not been "babied". But, also, it is not a wreck. I have been told that it could be a sensor in the front? I also know that the brakes will work, but the ABS will not. Although, on may way home tonight I was curious as to whether or not my brakes would lock up. I made sure there was no one else around, on a long patch of empty road, I accelerated to about 35 m.p.h., and slammwed on the brakes, and noticed that my passenger side front tire locked slightly.
Is this where my problem is? Do I replace that sensor? I got a price at the dealer today on a sensor....$143.00 for one! Also, backing out of my driveway earlier this afternoon, I had turned my wheels completely to the right as I was backing out of the driveway, and noticed that the ABS light had gone off...but only for a few seconds.

Any feedback would be appreciated!

I disconnected my ABS Brakes by removing the fuse. The ABS Brakes in my 99 Tahoe had a tendency to not stop the vehicle in time. My suggeston would be to check the fuse panel.

I would bet money that it is the wheel speed sensor. The only problem is, to troubleshoot it you have a few choices, you can shoot it out with a multimeter, take it to an auto shop, or buy one, slave it in at the spot you suspect, if it doesnt fix the problem go to the next wheel until the light goes out.