Joe Lacy wrote:
> I can replace the old sky with the new sky but I'm getting a white
> outline around the trees. How do I get rid of that?
>
>
I know you are inundated with all kinds of suggestions.
I have found one technique to look more natural and is easier than any other technique i have tried (so far). This is a quote from another post still on page one of this forum, by RobJames. I modified the quote a bit:

Open image with white or dull sky, Open same size image with good sky.

Copy and paste or drag the original bad sky image into the good sky image as a new layer. Bad sky image should be top layer.

Change mode on upper layer (bad sky) to darken.

If there are any details from the good sky image that are showing through where you don't want then make this layer active and paint out the unwanted details with white. (paint directly on the layer, no masks involved)

The same for the original image in that if there are grey or dark areas blocking the new sky then paint them out with white on the original layer.

Seems to work great on some images and so so on others depending on lightness and darkness. But when it works it is a time saver.