What you're experiencing is due to mass and rotational forces, at first it doesn't want to turn in (need to lean in), then when you try to exit, wants to keep turning. A few things might help, first is to make sure you've got optimum air pressure, too soft and it will really exacerbate this, next try to lean in vs turning in, those big tyres take a lot to get them to respond.
You could try messing with cockpit setup, but I'm more convinced it more a case of technique vs setup, especially if this is your first time on 3.0" plus tyres. Also, some tyres self steer really bad, while others don't show any signs of it, so tyre choice can play a big role as well. A lot of the time on my plus bike I'm leaning into the turn while applying pressure to my inside hand to keep it from turning in too much, this on a rigid 29+ with a 68" HTA, when I had it setup B+/29+ with a 67.4* HTA, I had to concentrate more on tight, sharp stuff or it would push the front.