I have a 2006 Chevy Malibu Maxx LT, 3.5 V-6 (I wrote about it before) that has a delayed and harsh shift from 1-2 and 3-4 to a lesser degree. I have checked all the sensors that my scan tool can read - VSS, load, TPS, etc. I changed the filter and there was no metal debris or clutch lining debris in the pan. I filled it with the correct fluid until it weeped out the check hole near the right axle. Once it engages, it stays engaged, downshifts fine, etc. I don't think it is a transmission issue, I believe it is the valve body. When the TCM sees a delayed shift, it is supposed to increase the line pressure to force the shift which is exactly what it appears to be doing. When it does engage, it engages hard. There are no codes stored so I don't think it is a shift solenoid or pressure solenoid issue.
So here'* my question - there is a first and second design on this transmission. If the car was built prior to 12/12/05 it would have the early design, after it would be the second design. The ID tag on the door has a manufacturer date of 12/05 (naturally!) so I don't know if I have the early or late design. Research has shown me I have the 4T45E transmission. I have found valve bodies but one says it is for a 4T65E but does fit my car. Is there a difference in the valve body between early or late 4T45E and/or the 4T65E and if so, how do I tell exactly which design I have? Is there an actual assembly date somewhere on the car or is there a number on the transmission that shows the built date (even better if there is).

Everything I find tells me this is a 4T45E. You can confirm by transaxle pan shape:

Pan shape is same as 4T4x. I just found TSB #1064 doing an on-line search and it says the correct build break date is Dec 13 2005, not Dec 12 which is Julian date 347. It also says that first design and second design valve bodies, spacer plate and channel plates are not interchangeable; there was fluid routing design changes. It also says the RPO number is MN5 for the 4T45E transmission. I will verify this then try to find the Julian date to see if I have the early or late version.

Where is the Julian date (build date) located?

The sticker in the door should tell man date.

Which will be different from the trans build date.

Duh...!

2006 Malibu MAXX transmission ID - I found the SRTA tag on the transaxle, unfortunately it is difficult to read and the numbers don't look like the pictures in the TSB I found. Here is what is stamped in the top right corner
3176
1
2
On the bottom of the tag is the GM emblem, with Canada underneath and a part no. 24221260. Does anyone have a list of transmission numbers that could tell the actual build date? They changed the valve body design on 12/13/05 Julian date 347 so I need to know when this thing was built. The door tag just says 12/05 so that'* no help.

Right, the door tag just says 12/05 so no help. And the trans most likely was not built the same as the car.

The trans tag is the only thing that will identify the complete trans build.

And those are casting #'*.

The tag is supposed to have a three digit Julian date in the upper right corner. Unfortunately, the printing is worn off but there is a stamped number 3176 with a 1 and 2 stamped vertically under the 6. I am trying to find the Julian (production date) so I know if I have the first or second design valve body. The change was made on 12/13/05. The only other choice is to remove it and look at it to see which it is by the fluid channel design.