speedometer issue the code reader is showing the output speed sensor is the fault, in park my scanner shows the VSS at 20mph so i took a look and it looks like it was replaced so i tried a old sensor i had laying around and it did the same thing, and tried another cluster as i had one and same result. any ideas?
When its in park the cluster shows 0mph while scanner shows 20MPH, put in gear holding the brake the cluster reads 20mph don't matter what gear R, N, D, 3, L. the transmission does not go into limp mode it drives fine besides not knowing what gear to take off in and speedometer works fine once above 20mph.

This van is a 03 GC 3.8L with 96K miles.

 

I forgot to mention that it only does it siting still, you start moving and its fine.

 

Figured i'd share the answer to the problem, Changed the alternator and all is good now.