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Discussion Starter · #1 ·
I stopped by my GMC dealer this morning to see about getting the transmission update on my '08 Acadia - build date May 22, 2008. He had no problem pulling up the TSB for the May 8 update. After a bit, the tech came out and told me that a "TCM Operating Software" update is available for my vehicle in addition to the May 8th calibration. There is an ID number for this update: 24249047, which supercedes the original software, which was numbered 24245??? (I don't remember all of the number). The tech told me that this update is readily available and would take just a few minutes. He had no other information about it, except that he believes it changes the shift points. Can anyone provide more information on this software update?

He went on to say that the May 8 update is "VIN specific", meaning the tech must upload information from my vehicle to Techline, who then downloads the new software which is tailered to my specific vehicle. He said this will take at least 2-4 hours, and they offered me the use of a car. He also stressed that this update could negatively affect city fuel mileage, mostly due to the TCC not engaging in lower gears.

The tech suggested I try the 24249047 software change first, which he said should have less affect on gas mileage than the May 8 update. So that is what I had them do. I plan to drive it a few days and see how much improvement, if any, there is. I'll post a followup later.
 

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shortly before the May 8th update there was another optional update that improved the tranny's tendency to shift 5-6-5-6-5-6 when around 65-70 mph on highways with slight rolling hills. Everything else remained the same. The new May 8th update INCLUDES the same fix to the 5-6-5-6 etc. issue but also has the improvements to low end drive ability with holding gears longer etc. which is discussed in the May 8th thread on this same forum. It sounds like the dealer gave you the previous optional update which will improve the highway driving but will do nothing to eliminate the bad low end bogging in the 35-50 mph range. The May 8th update is a miracle for me and makes the car so, so, so much better to drive. Fuel efficiency for me has remained the same as the negative implications of holding gears longer has been equaled matched by being able to drive the vehicle smoother with less abrupt pedal motion to get the vehicle to downshift to accelerate faster.
 

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Discussion Starter · #3 ·
I think what you have described is exactly what this update must be. I have noticed no difference since the update, but I have not been on the freeway. Based on the good results you and others have reported, I have made an appointment to get the May 8th update on Monday. Thanks for your reply!
 
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