Took my Avalanche on the beach for the first time today, put it in 4X4 and light switched but I got dang near stuck because the front end did not engage to give me 4x4. I could hear the transfer case switching and it went into four low the best I can figure from sounds. First thoughts are to replace the actuator on the front diff. Does this sound about right? I find it strange that no check engine light is on and that the transfer gear lights work but nothing engages. Thoughts?