This is my latest attempt to smooth out a looping gif.
I opened the video and split into two segments. This makes an exact transition point with no break in continuity.
Then I reversed the order of the clips. This puts the exact transition frames at the beginning and end of the entire video.
Next: Add a cross fade transition to the junction of the clips to blend the two segments.
Add the still frame that has the most steam "drama" and mask to reveal only the moving steam. Match the time of the still to match the video.
Add a sepia tone adjustment layer and match that time also.
Save for web as gif.

Then close this working video image and open the saved gif file.

I posted a video of this locomotive: http://www.youtube.com/watch?v=NdEeaJhUL2c&feature=youtu.be
Now the time line shows the animation frames. Select all frames (151) and change the duration to "no duration" to increase the speed. Save for web with this change. Done