6 SPEED AUTO TRANSMISSION ISSUE WITH SHUTTERING AND WILL INTERMITTINGLY SOUNDS LIKE WHEN YOU DRIVE OVER THE GROVES ON THE SIDE OF THE HIGHWAY AND SOMETIMES HARD SHIFFTING BETWEEN LOWER GEARS . IT HAS SAME ISSUE AS BEING ALREADY REPORT WITH GMC TRANSMISSION . I HAVE TAKEN TRUCK TO LOCAL BUICK DEALERSHIP AND HAVE THEM FLUSH FLUIDS AND REPLACE FILTER . ISSUE HAS REACCURRED . TRANS DS NOT SLIP FORWARD OR REVERS .