Can you post his readings? In this situation it seems most likely that his humidity is too low. Bump him up 10% and maybe a couple degrees. Have you thought of introducing a humid hide in his enclosure?
Also, in terms of the hissing, shed period is a stressful time for snakes and this may be amplified by the fact that your snake has not shed properly. Once you get your environment specs together just give him a couple days to chill out and lose the rest of his skin.
If the skin doesn't come off on its own, you can soak them in warm water and then use a warm wet washcloth to gently rub the skin off.

Also pics might be helpful