My first and now long term impression is "subtle" with the tune. Small throttle lag is still present. Not huge acceleration difference. Unless it's over 60 mph. The truck can actually really pass on the highway now.
But the biggest thing, IMO, is disabling the EGR and fuel mapping (less regens). Like I said in a different thread, I did my first oil change last week since installing the tune. The lube tech at the dealer said the oil didn't seem dirty at all. That's a significant improvement over stock to me.