It's not that the stock pistons suck. They are as good as you can for a cast piston. Forgings are stronger, but need more cylinder wall clearance and cold you have piston slap issues.
What does suck is the tune. For emissions reasons the transition from closed loop to open is delayed when you first dip into the throttle and you are lean in that transition.
Just don't tell the dealer about the non- OEM tune. With a stage 1, you can pick up a little power/torque too. After the rebuild/new short block just take it to an independent shop ASAP to do the deed...
P.S. The '04 has 3 different OEM tunes. The early ones were subject to detonation. The later ones have 2 degrees less spark advance.