When you go for a walk, are you doing a "structured" walk, making him heel and follow your lead? Or, is it a game where he's hunting, sniffing, marking, etc.??
We found that if you let your dog "hunt" when out walking, that gets them revved UP.
If you incorporate more "structure" to your walks (even if it's only for part of the walk), that can help focus the brain and drain energy instead of just amp'ing them up.
Denna was still a nipper at 8 months... it was less than when she was younger, but it took a LONG time for her to give up 100% on using her mouth to grab people and clothes. Keep at it! Lots of re-direction to toys, and you might need to up the negative consequences of puppy teeth touching skin. We would YELP really loud, and that was enough to stop the current nip and give us time to redirect to a toy... lots and lots of repetitions finally got us the gentle, soft mouthed dog we have today.