Hey JohnLube Gard or any other miracle trans fluid will not fix that type of problem. In EVERY case I've seen with these gearboxes when it refuses to come out of gear, If the driver stops the vehicle and kills the engine, therefore removing the load from the drivetrain, the transmission will pop out of gear with the pressure of one finger on the shift lever. Which of course proves that there is no inherent problem with the internals of the gearbox itself. If it ever happens again, you should try that.
Got stuck today sitting in traffic. Shut the car off and it was still stuck. Not sure what that proves but there you go