3.73 rear end for 03 3.8 V6
 

Would this gear set fit into existing 2003 3.8 l rear end? Do you just buy the gears or is there more to it?

Original Ford Racing Performance Parts gearsets for your 8.8 Ford Rear. This is a 3.73 Ford Racing gearset that includes pinion nut and shim set.

I guess not. I have a 7.5 rear end not 8.8. I am also wondering if the non slip would be better than just the ring and pinion replacement. Looks like you need to upgrade the speedometer gear too and a number of other parts besides the ring and pinion gears. Advice appreciated.

You have to replace the ring and pinion with the 7.5 and not the 8.8. Also you have to buy fluid and you have to buy install kit. On my 94 I just went and bought a complete 8.8 rearend from a wrecked 96 GT and lucked out and got gears already in it. In 1999 the went from a Speedo gear to a computer controlled one. There is a dallas mustang device that you till it what gears you put in and it recalibrates it for you. Hope this makes senes and helps.