Hi, 4 wheel drive only works sometimes on my truck. When it doesn't work you can't hear the transfer case shift relays click. Any thoughts as to what the problem may be? Thanks

 

The relays are pretty small, and even if you had one in your hand, you moght not hear it anyway, so chances are you are refering to the actuator that you can't hear. Maybe I am being picky, but a good description really helps.
If you are refering to the relays, then it would be safe to assume that the switch is bad. If the relays do energize it could be the actuator itself.
I do not recall if the GEM is responsible for t-case activation, but if the wipers are not funky, or the door locks are working alright, it is probably alright.
If you have a multi meter, you can chack the actuator for voltage to see if it is simply a bad actuator.