I notice that when I reduce throttle from 40% to about 25% there is a big reduction in power and the airspeed drops like a rock from 120 to 80.  I know there was a modified air file at one point, but is there a newer one for P3D v4?

I assume that you are talking about the 'standard' 208 and the patch is the same for FSX and P3D. http://www.carenado.com/CarSite/Portal/index.php?accion=update

The EX has already the modified FDE.

 

That's from 2012.  I'd like one for the for HD version.

The 2012 version is the HD version and it is the only one for FSX/P3D. The non-HD version is the FS9 version.

So, I am still having the issue when reducing power that the speed drops like a rock on the HD version. 

Also, didn't the GPS have traffic in it?  I don't see it.in the v4 version.  Well, I ended up getting the RXP GTN 750, but of course it doesn't have all the fields in it, so I switch to the C208 GNs instead.