On my '98 Blazer, I'm having an issue with my brake pedal having a LOT of travel, and the brake light being on. Fluid level is good, etc.
Because of some experiences I've had with GM ABS, I pulled the ABS fuse in both fuse blocks. The Brake light in my dash went out, and the ABS light came on.
Try pulling the ABS fuse on the inside fuseblock, and see if the brake warning light goes out. If it does, there might be some issues with the ABS pump. I'm thinking there is with mine.