2001 Gmc Jimmy

The front drive shaft from transfer case down turns, indicating transfer case is in gear. Front hubs are out of gear. When in 2 high you can hear electric motor on transfer case. Engages eaisly when put in 4 high, in 4 low makes a clicking sound. In June 2004 replaced 4 wheel drive switch and control module by dealer. Can anyone tell me what the problem might be. Any help would be greatly appreciated.