Tomp , i'm wondering if your last post just pin pointed your problem.
Sounds like your shift motor is slow or T/C needs oil ???? or something is making it shift slow. You said it was binding and hadnt unlocked after shifting out for a little while when you were going to the gas station. Probably it is shifting in slow also , maybe thats why it wasnt locked in when in question , because you had just shifted in at the bottom of the hill and it hadnt engaged yet by the top of the hill even though it was in low range maybe it wasnt fully locked yet. Just guessing.
