One other thing that I would like to mention here, is the fact that you changed so much fluid in a short amount of time. If the condition of your fluid was that bad, it had become abrasive! It had also caused a lot of scares in the bores of the valve body. These scares will be filled with grit for the most part, but when you added the new fluid into the system, it will clean out all those scares and allow your pistons to leak inside the valve body. Hince the reason you now notice the shifting has gotten worse!
For now, go out and buy yourself a bottle of Lucas Oil Transmission Fix. This stuff is not snake oil, believe me! I had a heavily worn valve body at one time and this stuff had my tranny work good enough that when I finally got the money for a rebuild, the shop could not find anything wrong! That was until I told them the stuff was in there and they did a quick drain and fill. This deluited the mixture enough to allow the leakage to take place so they could more accuratly determine the full stint of my problem.
Here is my testimonial! Try it out and see if it at least can help your tranny stay afloat until you can get your it reworked.