Spiritedmama --
I get the sense that your son is your oldest child? If so, it's important to remember that middle school is really different. It is very much about executive function and making sure your child is ready for HS. This is important work that has to get done. Making sure he has ownership of all his work, and that he can manage it all.
You spent the last 4 years at the GT school making sure your child wasn't bored and losing motivation, or causing trouble in school because he was bored, or feeling like an "alien" because he was so different from other children. It's not a race. If you have preserved your child's love for learning, then consider it a job well done.