1995 GMC Jimmy ABS Controller

Hi all, ok, long story short, my g/f owns a jimmy, and she was told the ABS controller was bad, and has had it unhooked for quite some time now. So the "ABS" light stays lit on the dash constantly because the contoller is unplugged. So today, just to see why it was unhooked exactly, I plugged it back in, and went for a drive, brakes worked good, "ABS" light went out, and when I accellerated to 55, then came to a stop sign, put my foot on the pedal, it was hard as a rock, and i couldn't stop. So I just kept mashing the pedal, and little by little it went down, and I got stopped, and then it was fine for a little bit. Ok, then I got out to go again, tried to stop, same thing, very hard pedal, that would loosen up if I continued to mash on it, and once it went all the way down, it would be fine for a little bit. So needing to make it home in one piece, I unhooked it again, and now the "ABS" light is lit again, but I can stop easily. Is this actually a problem with the ABS controller, or is it a wheel speed sensor? Maybe should the brake fluid be changed? It looked pretty black, how do I go about doing this with the abs? How hard is it to change an abs controller? What should I take into consideration? It is a 1995 GMC Jimmy SLT with the 4.3 V6, 4 door, 4 wheel drive. If anyone was wondering. Thank you.

bump

Something is wrong with your ABS valve portion of the braking system.

Get it to a shop to have it properly fixed.

Your model should be included in the ABS recall from GM. You have the signs. Talk to your local dealer about checking it for the appropriate recall service. If it has been updated then you will need to have it checked out/scanned. The other option is to check all your wheel sensors.