Tranny not as easy as it seems...
I have been having problems with my 2004 LS tranny and several people suggested that I check the fluid level. I couldn't get the dealer to do it, and frankly I didn't have the time to argue, so I took it to a mechanic I know and we tried the method described above and fluid poured out; it didn't drip, it ran out. The guy definitely removed just the center plug. I watched him do it from underneath the car.
All I can say is, be sure that the shop who is changing the fluid knows how to do it and that they have the right equipment. Although I found a 4-line description of the procedure on the internet, the mechanic had at least two pages of info just about how to check the fluid level, and he did not have the tools that were called for. It seems to me that it shouldn't be this hard!
But, the good news it, I think the problem I've been having may be due to too much fluid, all though I can't be sure; you just don't expect to have fluid pour out of the thing when the instructions say that it should just drip out. However, the car seems to be shifting MUCH better now. It was stuttering for a second or more at times, and it was shifting VERY hard at other times; now I've barely felt it stutter at all in the last couple of days.
I'm grateful that people on the list were able to give me some good info...