Hey Joe. To answer your question, it's possible. SHBG binds to testosterone and keeps it from being "Free." Free Test is one of the things that most Hormone Replacement Therapy (HRT) specialists look at because that's going to determine how you feel to a certain extent. Having normal test levels and low free test can be just as detrimental as having low test.
I would suggest getting in touch with someone like Chip. also, that's a pretty sharp decline in T levels throughout the day. I would say you have Low T my friend.