Pikachu during the fight in the gym Nimbasa seemed desirous to wreak brood anger. It might still got to do with Meowth's betrayal?

Mhm...It's a possibility. Or Ash made some faults in his strategy...

OR- well, of course. That could be it too. >.>

"Pikaaa! Do as I say, A GOOD TIME!"

I am sure the next time Pikachu will see Meowth he'll rip away his skin ..For this reason, there are many episodes without the Rocket. To increase the boil in Pikachu .. And we the waiting.

yeah thats true

"FOR THE POWER OF GREY SKULL!"

he wants to relese hie energy

But Ash has something different in mind...