1995 Ford F-150 transmission trouble?

I have a 1995 ford f150 4x4 with a 302 v8, automatic transmission, push button 4x4 144, 000 miles. I had a looad of coal on it, was backing up to shed to unload it in four wheel drive 4-hi when all of the sudden truck wouldn't move anymore. I lost all gears. Tried 4 hi 4 lo 2 wheel drive still nothing. Linkage and all wires still connected, checked all fuses and relays. Transmission fluid is full and clean, never has slipped, clunked or any other noises, no leaks, all lines are connected and are in good shape. Transmisson has also been regularly serviced. I talked to a friend he said he had a similae situation with a chevy truck with push button 4x4 and it ended up being the transfer case not the transmission. Could this be the problem in my case? Is there anything else to check or do u have any other ideas? I have a hard time beleiveing its the transmission because I have never seen one go so sudden, and with clean and full fluid and never slipping. Most of the time you still have some movement. Any input or ideas would be greatly appreated. Thanks