Join Date: Jul 2012
Location: Bowling Green, KY
Just to eliminate it as an issue, and start with the simple stuff, you are shifting into neutral and coming to a stop before attempting to engage 4LO?
You are correct that you must be in 4Lo for the rear diff lock to engage.
I'd try it again a few times, read the procedure in the manual and follow it to the letter. That will make sure it is an issue before you take it in. Mine is kind of picky about going in and out, but once you get the "procedure" down pat it works well.