Since you don't need a lot of rpm, I would find an adjustable timing chain kit and install the cam slightly early (3-4 degrees) to increase bottom end torgue. A 5.9 cam has more lift and duration than the 5.2, but I don't know if that would help you or not. Don't know if anyone did that kind of swap with good results. Gasket match, shortie headers, high flow exhaust, and a tune would be your best bet for power on the cheap.