just got an 04 cavalier and the ABS, Trac off and engine light are on. Occasionally speedo won't work and tranny shifts hard. Already replaced vehicle speed sensor per OBD-II code. what's up.... anyone??

Need to repair all the DTC's...ABS code is Anti Lock Brakes and sometimes the ABS system,the wheel speed sensors are used to calculate vehicle speed,and the Traction Control system is DEFINITELY controlled through the ABS system.The trans is shifting hard as that's General Motors computer strategy,if any kind of malfunction with the trans,the computer will jack up line pressure inside the trans,causing harsh shifts.So diagnose and repair ALL codes.