A few weeks ago my wife told me that the 4 hi and 4 lo lights would flash five times then stop, then flashed five times again after a short period. It did this for about 20 miles until she got home. I went out and tried the 4x4 and it didn't work in any setting, auto, 4hi or 4 lo. Made sure to put the truck in neutral with the brake on before shifting to 4 lo. In 4 lo the gearing is lower, and the front differential locks in, I can hear it and feel it on sharp turns. Have not seen the flashing for myself because it hasn't done it since my wife saw it. The indicator lights are working properly when changing the switch position.
Took some advice from another thread and tried cleaning the front speed sensor. That didn't help. I also noted the position of the shift motor, I had left it in 4 lo before starting work. Next I replaced the front speed sensor, this time leaving the switch in 4 auto. Replacing the sensor didn't help, and also noticed motor in different position which tells me that the motor is working.
Does anyone have any idea what else could be wrong. I am not having any other problems with the truck electrical, or otherwise, so i don't think its the GEM module.
Please help. I don't have a wad of cash to pay some dealer.

 

Mine got stuck in 4wd low, so I proceeded to hit the transfer case with a rubber ended hammer. WORKED!, It shifted out of low and worked fine. Mine may have been a fluke, yours sounds more serious.
Good Luck,
Joe