Creating an engine's specs (Dev's Needed)

Im trying to create the a bus engine's specs. The bus engine is a Cummins ISB 6.7L Turbo I want the torque curve to look like the picture below and have the same 800 lb-ft @ 1,500 rpm, 350hp

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The transmission is a NV4500 2001, I have the gearing set to the specs outlined in red in the picture below.
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Although I have everything setup right, my engine only produces 640 lb-ft @ 1,500 rpm and 162hp...

Creating an engine's specs (Dev's Needed)