key locks in ignition..

 my key locks in the ignition.  I have had it into the chevy dealer 4 times and they can't find what is wrong.  It doesn't always do it just enough to drive you crazy.  If I take the gear shift and go through the different gears and then go back to park it unlocks and I can take my key out.....

Sounds like a intermitant shift lock. Saftey feature that will not let you remove the key until the trans. is in locked into park.

thanks Smash.....I am going to my Chevy dealer again in the morning.  I will give them  your idea.  I have noticed lately if I really shift the gear into park with force, it is ok....thanks again.