Toyota did something new to the 2009's which I believe they thought would mitigate the bottoming out issues. Obviously it does not. See my post here about that.
Anyways, I had the TSB completed on my 2009 4x4 OR DC in September 2009. My problem report was simple. I was bottoming out with my camping gear in the bed while driving on a gnarly back-country service roads. I knew something wasn't right and did some searching and found TacomaWorld and the rest of you good folks.
I read about the T-SB-0305-08.pdf for the rear springs, and it seemed like it would solve my problem.
Next I verified the parts numbers for my factory leaf packs were identical to replaced parts in the TSB. The part numbers are on the top of the springs.
I took pictures of the underside of the truck bed to show where the bump stops were hitting.
It was very clear I was bottoming out because it was dusty as hell everywhere except where the bump stops make contact. Duh? this should be a no brainer. I printed the TSB and went to the stealership.
I explained that I was having a harsh ride and bottoming out in the rear while driving on back country roads with a load in the bed and that I found a possible solution and gave them the TSB number. The service adviser was like yeah, yeah, yeah, and gave it to his service tech.
I explained to the service tech that the part numbers on my Tacoma were the same as the ones referenced in the TSB, and I simply suggested that it may solve my problem. The dealer service tech gave me a bunch of lip about Toyota will never apply the TSB to my '09 because it was not officially covered. I simply smiled at him and walked away. [The 2010 and 2009's are now covered.]
To make a long story short, the approval for the TSB came not from the dealer but from a regional guy who works for Toyota and services the entire southern California region.
Here is a picture of the new leaf pack
Well, I can say that the rear end is stiffer and that is exactly what I wanted! With no load in the back, and driving aggressively on pavement I will occasionally get what feels like wheel hop in the rear. e.g. accelerating through a steep depression, like just before climbing a very steep hill. But that is rare and I drive conservatively.
I bought the truck to access the many remote areas of the southwest while camping and climbing. After four months of wheeling I can say confidently that I feel that my truck is much better equipped to do that now.
However, based on how I use my truck I don't expect the TSB springs to last beyond three years, at which point I'll probably go with some custom springs.