car wont go into 4th gear shifts 1st 2nd 3 rd not 4th- overdrive.

Assuming you have the 4T60 (4 speed) and not the 3T40(3 speed) transmission, I'd check adjustment of the shift cable to be sure the transmission is actually in drive. You set adjustment with the transmission in neutral. Lift the shift cable lock button up so it releases the cable. Manually shift the selector rod on the transmission to neutral. Next, shift the selector (shifter) into neutral. Last, press the shift cable lock button to stay the cable into the new adjusted position. If that does not work, we'd be happy to take a look; just contact us for an appointment.