Doe's this look realistic? Taken from Hughes engines
In our opinion, the greatest restriction to making more power in stock magnum engines is the camshaft. It is not little, it is teeny weeny. The chart below compares the stock (5.2/5.9 - they are the same) cam to our smallest 5.2 torque cam.

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Using our SER9703AL cam in a 5.2 engine a customer reports an improvement of 23HP and 35 lb/ft of torque @ 2,000 rpm at the rear wheels. Using our SER0814AL cam in a 5.9 engine a customer reported 48 lb/ft of torque @ 3,500 rpm and a 31HP gain @ 4,700 rpm at the rear wheels. These changes are with a cam, lifter, timing chain and springs only.