Need help with Crown Victoria speedo/odo problem

My daily driver is an 09 Crown Victoria/P71.  A few years ago the rear axle was swapped, I believe these had a 3.27 to 1 (?) rear axle and the new rear axle "appears" to be a 2.73 to 1.   My indications ?   After the rear axle  (that my mechanic assured me came from another P71)  was swapped in, the car didn't seem quite as quick as it had been, which is no big deal.   But I noticed that when I was going what my speedometer showed was 40 MPH that I  was passing everything else doing what I assumed was doing 40.  Also, when I pass signs on highways that say  " your speed is "  my speedometer shows 35 and the sign says something like 41, 42.

This also has affected the odometer.   Mile marker signs on interstates say that I should have gone 10 miles, but the odo says about 7-8 miles traveled.

It is getting to the point that it is annoying to have to do the mental math conversion.

So, if you have read this far, is it possible to correct this with some kind of electronic re-scan ?   Or does this require some kind of part from the dealer ?

I'm not an expert on the 2009 version of that transmission, but I'm guessing either it has a speedometer gear in the transmission (the earlier versions do) or you can use a tuner to input a different gear ratio.

It should be a programmable parameter in the instrument cluster. 

In reply to Saron81 :

If I go to the nearest Ford dealer and explain the situation will they be able to do that reprogramming at a reasonable cost ?

This car has a few " minor " problems, and I am thinking of turning it back in to the charity that I bought it from.  But even I have found it mentally tiring to constantly monitor the speedo and then do the math as the speed differential increases (widens) as the actual speed increases...you don't just add a flat 7% or X%.