My 2003 ZR2 four wheel drive transmission drops out of gear
 

My2003zr2 4x4when it gets to operating temperature can you driving down the road and you let off the gas it will drop out of gear you hear a loud clicking type grinding noise in the transfer case the transmission free wheels you rev the engine up and it don't pull any more I have to pull over to the side of the road engage and disengage into 2 high and 4 low until finally go back into gear and I have to ride around in 4 low to keep it from dropping out of gear

Probably should not be driving in 4WD all the time unless its an AWD instead of 4W, which based on it having a 4Lo and 2Hi option its not, Start at the transfer case since it will cause much of that clicking noise, and check for a stuck Throttle Valve while your under there, chances are the Tcase will need to be rebuilt since they tend to be fragile from that era and running it all the time with city/highway driving will wear it out quickly. The tranny is dropping out of gear probably because there is no rotation on the driveshaft, so its down shifting to match what speed it thinks your going and you've let off the throttle, Im no expert especially on 4L60Es (which im assuming yours has based on model year and type of vehicle) so i very likely could be wrong on that part