99 Grand Marquis, what do I need to go to 3.55?

[99musclemerc]

Well I'm working on a 99 grand marquis and I'm wanting to a 3.55 ring and pinion. I happened to pick up an alluminum shaft at the yard but not sure what version it is, it just has "police" printed on it. Do I need to tune at all or can I swap to the 3.55 gears on a stock setup? also can I use the aluminum shaft on the tailshaft I have now or do I have to have that longer tailshaft? Anything else I could possibly be missing?

[Rob Roy]

Your shift points will be off with the 3.55's and the stock PCM. As for the driveshaft, you need to swap in the extended tailshaft to use the CVPI aluminum shaft. Regarding the tune, if you don't mind giving up the PATS functionality, you could swap in a '99 P71 PCM and speedo gear and be good to go.