Brake pedal can't be pushed down when abs comes on, 2002 silverado

SOURCE: brake and ABS warning lights on, trac off on.

You may have a bad abs controller. You need to get the code for the abs light from a shop or auto parts store.

SOURCE: brakes grindind at low speed

Sounds like your getting abs activation when its not needed. Most likley one of the wheel speed sensors has failed. You do need to have a scan tool to read the live data from the abs module as the problem is occurring to pinpoint which sensor is faulty. The abs light will not come on because the abs module thinks its just working normally. I'm an ASE certified mechanic and have seen this problem many times on various vehicles. You might have to pay somebody to diagnose it, but replacing the sensor it a very easy task. I hope this helps.

SOURCE: Abs/Brake Light ON, although new brakes, ABS still works

I would suspect a speed sensor.

SOURCE: antilock brake system engages on low speed stops on dry pavement on my 2004 Silverado

Very loose front wheels bearings can cause this.

SOURCE: 1999 Chevy Tahoe- Soft Brake Pedal

Try having the dealer flush and bleed your system. It is very hard to bleed ABS systems yourself and have safe brakes that still work afterward. Bleeding non-ABS brakes yourself is easy not the same for ABS brakes. Valving, sensors and what-not require a tech and the correct equipment in my opinion. You do it wrong and you could ruin your ABS system. Do that and see if they firm up. I replaced my brake shoes/pads at the same time all new everything in back, drums/springs everything and new rotors up front. then I had the chevy dealer flush, refill and bleed system. Stiffer pedal and brakes work better. Keep in mind the brakes on 99 Tahoes are inaedequate, require new rotors often, heat up and fade/glaze pads regularly. I replace my pads long before they wear down because they glaze up and start fading early. I'll rough em up once maybe, next time, new ones. Every two brake jobs, new rotors for me. Just how it is. They will stiffen a bit and work better but they will never be awesome brakes. Just how it is on 99 and earlier Tahoes. Hope it helps. Very important to bleed correctly though. I'll bleed my 83 Toyota 4x4 myself but not the Tahoe.