Max HP and Torque from an ISX CM 2250 CPL 3917

[Mike in NC]

Hello,
I am trying to help a friend out. He has an ISX15 CM2250 CPL 3719. He is looking to see what the max HP would be, without having base engine issues. He has been told 450 HP and also 500 HP. He says that it has little lower end power when trying to merge on the highway, even with 20-30K in the box. Any information would be helpful. He mostly runs mountains on east cost of USA. Usually around 40K in the box. Thanks in advance!!!