Rick, there's been more than one guy who's run a 5.9 on a 5.2 tune--stock for stock. the open loop tune (WOT) is so rich, that a stock 5.2 tune does just fine with a 5.9, especially when you consider that the 5.2 has a bigger cam than the 5.9, and that their actual power output is only about 25 hp apart from each other. then when the computer goes into closed loop, it's reading the AFR through the O2 sensors in the exhaust, and will automatically tweak the fuel trims to keep it from going lean.

I'm not saying that it's "right" or that the computers are the same, only that it can be done without hurting anything and will get you up and running