Just put my 2004 Trailblazer in the shop. While driving it feels like even though the speedometer is on 70 steady without moving the tach very slightly jumps up and down just slightly. sort of feels like your stepping on the brake and then releasing it while your driving. The dealer said it was the oxygen sensor and the throttle body needs cleaning, which is probably what caused the sensor to go bad. Total $369.00 plus tax. Anyone else ever have this problem?