2006 Sierra

There is a safety lock out that will not allow you to put the truck into drive on some models not even move the shifter out of park.

There should be an override around the shifter with a small cover that you remove and use your key to disengage the safety lock.

There may be some variances in the safety lock out that they are generally time to the brake pedal.

Push on the brake pedal and see if you can hear something moving in and around the shifter. Also look around the brake pedal for a linkage arm which can be worn or out of adjustment causing this problem.

I hope this helps.

I think what you are maening here is that it will shift into 1and 2 while drivign but not into Drive. If that s the case then taek it to a trans guy as it may be a shift valve bad or a wiring problem. He can scan it and see if everything is ok with it or not. It also could be a trans problem as well like a clutch or seal bad.

I did misunderstand. I hope I did not cause you to waste any time. Hmac is the expert and I thank him for the help.

It sounds as if the trans is toast. Especially with the slippingpart. And Overdrive not working. You didn't need to takeit to a dealer, thereare many qualified independent trans shops around as well.