1995 jimmy 4.3 4x4 problem

1995 jimmy 4.3 4x4 im having a problem with the 4x4 the jimmy will shift in and out of 4low but when i try and do 4 high the light comes on but doesnt go in gear. If i play with it sometimes it will pop in and start working and other times 4 low and 4 high just flash. I tried disabling the battery and resesttig the tranfer case but same problem only works sometimes then i have 2 do it again any advice on the problem thanks:banghead: