Great write up! I just installed a similar trans kit this weekend. I bought the intense kit which included a few more spacers, springs, piston seals, filter, gasket and assembly lube. It is twice the money however but from what people describe the end result in shifting is similar. INTENSE-Racing.com: INTENSE⢠Street/Strip Performance Shift Pak®
The one thing that I would note is to be cautious with a trans flush on these cars.... especially with high mileage and no service records. I've spent a lot of time reading 3800 forums and have had several of these used w-body cars. In an older trans that has not been serviced the dirty coloration in the fluid is clutch particles and can be needed to get grip between the worn clutch rings. If you flush all of the old fluid out the trans it can start to slip soon after the service. Most experienced 3800 people suggest just dropping the pan, changing the filter and topping off with the fresh 8 quarts. On a trans that has really dirty fluid and starting the act up 7 quarts of trans fluid and a bottle of lucus trans fix usually will give some extra life to the trans.
I don't know how many miles were on your trans but if the car has higher mileage I'd guess your trans has been serviced in he past. Your pan looks about as clean as I've seen so I'm guessing someone either took it really easy on the car and it has low miles or the trans has been serviced before. I've done a few pan drops on higher mileage of these cars and the pan and magnet is coated with grey crud. Just my 2 cents but great write up and pictures!
Op mentioned a more or less trans fluid exchange not a flush a pressure flush is what screws **** up. But letting the fluid run out while putting new fluid in won't kill it, as its the same principal as dropping the pan.
06 GXP | 222/227 cam/cartuning turbo kit on 8psi/meth/e85 coilovers/ still on stock trans at 130k