The Magician's Tower

So with TBS spells becoming craftable I finally got my level 75 RS pet. I love him, he hits harder, lasts a little longer, etc.

My question though regards his AI. with the old RS pet I never had an issue with him switching targets. He would just beat on whatever I pointed him at, and once it was dead he would attack something else if it was beating on me, otherwise he'd just wait around and poof. This new pet doesn't seem to work that way. I grind AA on the Katta elementals at the little mini-temple often, and when I pulled him out there yesterday I found him switching targets fairly often, sometimes not even making it to the mob I sent him after. I usually pull 3-4 at a time to maximize the effectiveness of DS and burning aura.

Did anyone else notice this change when going from the 70 to 75 RS?

As far as I know, they all act the same.
I have seen the switching you mentioned. I believe several things can happen.

1. Just as you are casting RS on 1 mob, another mob hits you with a spell and RS auto-aggros on the one that hit you.
2. RS switches to a low HP mob, then switches back.

What Zac said.

Especially with the weak elementals, it's not hard to have a few at low health at once. RS will switch to a low HP one to finish it off before resuming on the original target.

Yes RS is supectible to low hp aggro, like a normal pet not under /pet focus.