I just upgraded my 2017 4113 to two 6 volt, group 27 AGM batteries. I was receiving conflicting information so, before I upgraded, I contacted Progressive Dyn. to verify the 4500 would have no problem handling them. They confirmed it would with no modifications. So, as Grumpy said, if they are truly AGM then no problem. When I contacted PD, I did so by email and they responded back within 24 hours. So, if you still have questions or doubts, contact PD.
Another advantage to going with AGM you can lay them on their side, making it easier to get to the terminals since they are in such a tight spot.
2017 Jayco Seismic 4113
2016 Silverado 3500HD 4x4 Duramax