Can't get it into gear!

Every once in a while, when starting my 2000 5.3 Silverado, I cannot get it out of Park. I have to get out and rock the truck back and forth before it eventually will shift.

Anyone know what this is all about?

I also just heard an AAMCO Transmissions ad on the radio that says rocking a vehicle can damage the tranny.

Thanks for any insights.

My 2001 does that too. Too much pressure on the park peg that goes into the flex plate. Any kind of a hill causes this... the fix... Apply your parking brake before you put the truck in park. Then put it in gear before you release the parking brake. Hope this works on your truck for you as well!