I have an 02' 1500HD. 6.0 Liter, auto trans, 4X4,with 96K miles on it. I was parked on a gentle slope - less than 5% grade. My truck was off and in park - no parking brake set. There was snow on the ground as well.

As I was standing waiting for a friend to open their door, I heard the truck start to move. I looked back and it was rolling, not sliding, backwards. I ran over and jumped in and put on the brake.

Do you think there is a problem with the tranny? Ok, so probably a dumb question, but any ideas on what it might be?

Thanks!
Dave

 

Your 'park gear" may be out. And to tell you the truck I dont know alot about trannys, but I believe that cirtain gears can go out while others still work. I just replaced my tranny for $1200 if you want to go that route.

 

Probably have a worn parking paw.

 

I agree it most likely is the parking paw. The problem is this could be an indicator of more bad things to come. The longer you prolong this, the worse it's going to get. So get it fixed soon before you kill someone, or your truck! Good luck bro!