Check Engine Light On 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?.