It will all depend on your CPL code.  If you give a Cummins dealer the code, he can tell you what they can turn it to.  In my experience they will not go past the CPL rating probably because of liability.  The CPL takes into consideration the type turbo, pistons, transmission and differentials. The software to set hsp. is fairly expensive and some shops don't spend the money for that, however Cummins dealers will prob. have it. If you have the right CPL they can be turned to at least 370.