Chevrolet Repair: Tahoe brakes, brake caliper, mechanic shop

Question
Hello.  I have a 99 Tahoe whose steering wheel shakes pretty violently when brakes are applied if the car is rolling.  The alignment seems ok, in that it doesn't wander or wear the tires unevenly.

I think I have ABS on this Tahoe, but I could be wrong.

Is the shaking due to warped brake discs, or is the likely culprit something else?
Thanks!

Answer
The shaking is a pretty good sign that the rotors are warped. You should be able to pull the rotor off when you take the brake caliper off to change the brakes. Once you have them off you can decide to either get those fixed or just buy new ones. If you have a machine shop or just a mechanic shop around, it should only cost 10 to 15 dollars a piece to have them turned(ground back to smooth).