Pretty sure he'll be soaking a majority of the exp from ya. And if you kill things that he doesn't receive experience for, you won't either.
Other than that;
Najena? Random mobs in Dagnors or even one of the gobbie camps? Maybe Runnyeye, haven't had any experience with it on p99 but the lower levels in there might be some exp for both of ya. I'm sure you could find a few spots in Kunark but I prefer the mainland areas.
Just a few of what I assume to be many places.
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Good luck!