I think Azcowboy  has the right Idea....With my GIII+ set to NAD83 I can set 
my DDD MM.MMM to any other co ord setup.....and when I Upload co ord in  DDD 
MM.MMM and Im set to DDD SSS MMM I end up with a very different set of co 
ords that I dont think is the mathmatical equivelent. Id make sure you are 
set to DDD MM.MMM