I got this info from the Acura TL forum and it also applies to our van's transmission as well - they are the exact same transmissions.
For those of you who may be experiencing transmission issues such as delayed shifts, slow shifts, harsh downshifts, or anything of the sort, you may want to try this simple fix.
It is somewhat common knowledge among Honda transmission experts that the most common failure point on these units is the 3rd and 4th gear pressure switches.
It is a good idea to change these every 100K miles or so and will often fix any problems that you may be having. I just changed mine and it made a world of difference.
Here are the part numbers:
These are parts # 10 & 11 in the diagram and are very easy to get to from the front wheel well.
Also, I would highly recommend getting the factory Honda Z1 ATF out of there - it has too many friction modifiers and will eventually cause the friction plates to wear out prematurely. I recommend Redline D4 or Amsoil.
For more info, check out this discussion: