yup. I know what you are going through. Our 2004.5 duramax 2500HD crew cab was replaced with the exact same configuration 2015.5 the 2015.5 is 2 inches higher than the 2004.5. bed height, seat height, etc. etc.
And the factory nerf bars, while fine for us, aren't fine for my older aunts, uncles, parents etc. On the 2004.5 I didn't even use the nerf bars to slide into the seat. on the 2015.5 I need them.
One thing you might look into are the electrically operated bars that retract when the door closes and extend when the doors open. these often come down lower than the factory nerf bars and may solve your problem. But they aren't cheap!