97 chevy transfer case keeps kicking into neutral
 

i own a 97 chevy 1500k excab step side.. i love the truck but im stumped with it.. while driving if i hit a bump or sometimes even when i just put it in reverse it kicks the transfer case into neutral.. i have to turn the truck off to put it back into 2h and then it will work again.. unless i try and reverse (it will just kick back out). i can use reverse but i have to be gentle and try and try until it works..if i have it in 4x4 it seems to work fine....some one please let me know what i can do to fix the problem