More auto tranny questions

This is my first auto truck and I am looking for some answers so I thought this would be the place to get them. I've searched this site but haven't found the solutions to my questions. I have a c15 with a 10 speed Ultrashift. I wanted to bump up the horsepower to 550 from 475. The Cat tech said the transmission wouldn't take the extra torque. Huh? Is that true? My second question is, how do I make the Jakes engage in the lower gears? They only work in 7-8-9-10. I need them to come on in the lower gears too. This is a 10 wheel dump truck, and I come down some pretty steep mountain roads (dirt) when I'm loaded heavy and I need the Jakes when I'm crawling down these. Is this normal and how do I change this? I sure could use some answers. Thanks.

 

Hmmmm. I think I might have stumped the band.

 

Thanks a lot! I will check.