The only time this message would come on during normal condition (without a actual problem or malfunction with the trans) are
- Shifting the trans from park or neutral to drive or reverse while the engine is not at idle.
-Shifting the trans from drive to reverse or reverse to drive while under load throttle around 25% (as if you were rocking the truck to get unstuck)
-if the transfer case is in neutral or the tcm thinks its in neutral (has there been a service 4wd message?)
-shifting from reverse to drive or drive to revers while still moving, driveshaft moving more than 300rpm in either direction.
- low atf fluid or lack of prime (have seen one case of the pump would loose prime after sitting, had to replace trans pump)
- low atf temp below -49 deg f
Problems that could cause this message to come up as a result of a malfunctioning part and would require repair. Would have to go to dealer to check for DTC's
- Low voltage on a ecm circuit. there is a info bulletin out this #pip3413a
-turbine or output speed sensor failure
-park neutral switch out of adjustment
- there is also a clutch failure, but you said it woks fine after initial gear select so thats probably not the case.
The PI involves taking a scan tool while the problem is happening and watching the voltage on the tcm, if you have no other problems except the trans this may not be it.
As far as the bulletin #02-07-30-011C this involves the park/neutral switch with 2 connectors. The switch is on the drivers side of the trans you will see the shift cable attached to a leaver in front of it. if you have a switch with one connector this dose not apply. the switch is sealed and cant be taken apart. as fas as adjusting it, to do this correctly there is a special tool to hold the switch in the N position. A new switch will have a similar tool installed.
I would have the shop check for any codes that may help narrow down the search for the problem part, depending on his scan tool he can observe the voltage as in the PI and also check the park switch data to see if it matches where the shifter really is. The key is checking all this data while the problem is happening.
The codes should point us in the rite direction, and if they have anything to do with the switch it may not be a bad idea.