Brake Antilock Wheel Speed Sensor problems of the 1996 GMC Savana

The vehicke had to have the engine heads reworked due to engine check light coming on starting at 2000 miles. #1 cylinder exhuast valve was sticking open. We have had the dealer replace the window motor control motor and switch. Failed 4 times. Brakes are terrible. Although abs right front wheel will lock up, dealer can't seem to correct. Fuel pump failed in August 1998. Speedometer was acting up, would move 4-5 miles per hour at a time, not smoothly, would jump up or down. Cruise didn't work well. Dealer replaced speed control sensor in August 1998. Drive gear for speed sensor came apart inside transmission on 12/31/98, leaving us 800 miles from home on news years eve. Trying to get reimbursement etc from GMC. Started asking for help on Monday 1/4/99. . . . Promised a phone call back on 1/5/99. . . No return call . . . Called GMC on 1/6/99. . . Promised a return call nothing as of 5 pm est. We want to have GMC buy vehicle back under lemmon laws. . . . How do I proceed?.