[atalas]

It is a bit bright Bill,you probably didn't set the shadows end properly as you stretch .

Was this shot in light polluted skies or a dark site ? If It was try and use a LP filter( IDAS-LPS is good choice) because this will increase your dinamic range and help keep gradients down.

I would say you have a huge slope on the shadows end of your histogram which you don't want,and is telling you that you have a bright sky.

If you've stretched your backround that much you have taken away brightness levels that should of been allocated to other areas in the image.

PS only reads "255 brightness levels" meaning different shades of brighness and when there not allocated in the right place, other places don't get the brightness they need and you start getting a washed out look which leeds to low contrast in the image.

This will prevent your image from popping well and you end up with that very flat look.

So looking at this we see that too much brightness has been allocated to the background so that means that other brightness areas don't get what they need.
It is a very good shot Bill ! well processed and probably only these few issues are preventing It from being a great image.

Well done mate !