2005 2500HD with 36K miles just bought by a friend. In the last three days he has noticed that it *gets stuck* in Park. This happens when he is on level ground or an incline. If he turns his engine off, then re starts he is able to then shift. I am not sure if this is an Allison problem? Electronic? Stealership so far has blown it off, but he has an extended warranty, I wanted to know if anyone is aware of anything special that should be checked? Thanks for any help