What all does the PCM use the MPH reading for? My PCM is 5 time higher then my spedo

I am wondering what all could be affected by my PCM reading a speed that is like 5 times higher then my actual speed (which is what is on the speedo). I am thinking that at the very least it is kicking off my fans earlier and possibly other things that are based on the speed of the car.

Also, doesnt the speedo get its reading from the same place the PCM does? The car has a mail order tune, but should only be modified for my 3.73's.

Any ideas?

Mainly the shifting of an A4 tranny. I don't know why it's reading different, the source is the vss.