Brake problem like stepping on rock,have to pump to activate

Sounds like your brake light switch is bad. It is located on the brake pedal arm.
Amazon com ACDelco D891A GM Original Equipment Brake Light Switch...

sounds like a sensor about to go... MAP sensor ... or the TPS even ?

You probably have air between the master cylinder and the abs pump. Fill the reservior and have someone pump the brake and bleed the primary lines at the abs pump. Good luck.

My Dad had a 1999 Silverado that did the same thing, it's a bad design. You wont run out but keep track of your miles, Then you know how far you can go.

This perfectly describes a failure of the brake vacuum booster.
Replace the power brake vacuum booster.

I would try some starting fluid in the throttle body. If is runs with you spraying starting fluid, then you know its a fuel problem. If it turns out to be a fuel problem its probably the pump. You would need to then check for power at the pump.

Unfortunately the ABS relay is built into the EBCM. Electronic Brake Control Module. That is located on the frame rail, left side of vehicle and sits on top of the pump. Both parts are likely to be replaced together as getting the module off the pump can be difficult. I recommend a repair facility do this job but it can be done at home. You will likely need to take loose metal brake lines and that can be quite a task also.
Are you getting a code for the relay / EBCM?

Good luck
Please rate my answers if they helped.
Brett

try www.autozone.com to see if they have your car listed for diagrams pictures and step by step instructions if your car is not listed then try your local library they have all the car manuals and even copy them for you

There should be an emergency release lever under the dash on the pedal itself.Be careful,they come loose with a bang & can cause serious damage to fingers.Good luck,
ChevRev

you can order it at some dealer ships . it cost about 150.00 dollars or more.