You only need to remove the trans if you are installing the pump spring, which isnt really necessary unless you are planning on constant high rpm runs with it... most of the performance pack can be done on your back taking a trans fluid bath dropping the valve body...

 

I bought a 4x4 Yukon back in April. 1-owner, 125k miles & now @ 128.5. I was trying to order the upgraded servo to replace the stocker when I R&R the trans filter & fluid as part of my maintenance schedule but I had a trans tech talk me out of it when I was calling around asking questions 1 day. I was told that boosting line pressure (Sonnax .500) and firming shifts on a high mile transmission would hasten its demise. I have read forum threads that would confirm this line of thinking.

Since this his truck is my daily driver and I have no ambitions to rebuild or replace the original trans, should I leave it alone? is the transmission guy correct or does the firmer shifting extend the life of theses units? The 1-2 shift and 3-4 shift is very drawn-out on my truck.