I don't think it caused any changes in power since both years were rated for the same hp and tq. It was meant to change the sound of the turbo. Hence the 03 turbo having the desirable whistle.
I pulled this info from a Ford book I have saved on my computer that lists all the changes to the 04 model year:
Turbocharger Exhaust Turbine Wheel
• Three fins have been added to the turbine
wheel of the turbocharger.
• These additional fins were added to the
turbine wheel in order to improve the
turbocharger’s sound characteristics
A forum community dedicated to Ford F-series owners and enthusiasts with a Power Stroke diesel engine. Come join the discussion about performance, bulletproofing, modifications, classifieds, troubleshooting, maintenance, and more!