When hooked up to a diagnostic tester it says these codes. PO 128, 442, 455 ( 3 codes).
My car shifts good from first too second than prematurely shifts too third. on 2004 Buick Rendezvous
P0128 Is a coolant temp code probable thermostat and coolant sensor problem this may cause some issues if vehicle is not going into closed loop. and 442 and 445 is emission code which has no relation to your symptom. Have transmission checked as well. Have transmission checked as well.