While out driving, I put my 2004 Chevy Trailblazer LS into park and when I tried to leave the restaurant the shifter would move but the vehicle would not shift into any gears. I checked the linkage and it was attached. The truck could be manually shifted from underneath and you could then shift from reverse to neutral to drive. But every time you put it into park, it would drop out and the shifter would move but not go into any gear.

 

Check the bushing for the shift cable at the shifter end. You'll need to remove the boot.

 

Either brake pedal switch or neutral safety switch

 

did you figure out how the problem was?