Sounds a lot like a torque convertor which has been covered several times...the following is an email I sent the dealer I bought my car just a couple days ago. My car goes in Wednesday to have the TC looked at.
Joe,
First, thanks again for taking the time to go on a ride with me - unfortunately I couldn't recreate the problem I've been experiencing other than the sloppy/clunky 1-2 shift at very low rpms after the car is warm. Below I've included the email I originally sent to Joe:
I purchased a 2012 Cadillac in the middle of February from you and wanted to contact you in regards to an issue I've noticed to see if you could share this information with the service manager to see if he could give me a call to discuss.
In the last few days, I've noticed a stumble/vibration during light acceleration. It seems more apparent when the car is up to operating temp. Since I drive on the turnpike nearly every day, I really notice it if I'm going about 30-40mph and lightly accelerate (as if I'm merging onto the highway) - the car seems to stumble/buck as it accelerates - it's not smooth and just doesn't feel right. I can eliminate the stumble if I give it a bit more gas and get the RPMs higher, but if I can't accelerate more quickly, and the RPMs remain fairly low, it will continue the stumbling until it reaches the next gear or the RPMS increase.
I am by no means a certified mechanic, but I know a decent amount about cars and had my suspicions - after a quick Google search for my symptoms, the very first page that came up was the following:
http://www.cadillacforums.com/forum...sigh-bad-transmission-shudder-new-2012-a.html
Pretty much every post on that page mimics the symptoms I am experiencing and confirms my initial concern of a transmission/torque converter issue.
Obviously the last thing I want is my "new" car already in shop within a month of purchasing, but the stumbling/shuddering is pretty annoying.
Obviously within the email I sent to Joe is a link to a Cadillac Forums page where others have had the same experiences which were resolved with a new torque converter. After a bit more reading, I found that although GM didn't issue a recall, this problem is by no means uncommon. Attached below are a few more links to forums of many people experiencing the same issue and a TSB which seems to have been issues sometime in 2012. Simply searching "2012 Cadillac or Camaro Torque Converter" yields many pages about others issues. I've attached some below.
1. The following link is a similar issue found in the Cadillac ATS of similar years. On the fourth page (which is the link provided), a user posts information about a TSB although I was unable to locate it online. Most of the people in this 4-page thread seem to have had the problem solved with a new torque converter.
http://www.cadillacforums.com/forum...-vibration-under-moderate-acceleration-4.html
2. The following link is a Camaro owner with the same problem that was diagnosed as a torque converter:
http://www.camaro5.com/forums/showthread.php?t=213173
3. The following is a 7-page thread of numerous people experiencing the same issue. Several members claim to have had their torque converter replaced. He states that the techs couldn't find a problem running the tests, but did notice the problem on a road test. This page also discusses the idea that there was a bad batch of these converters and the "newer" converters are upgraded. On the second page (which is the link I provided), the member who had the issue solved with a new TC posts the document ID number and the technical number.
http://www.camaro5.com/forums/showthread.php?t=211490&page=2
4. The following is a link to yet another site with several Camaro owners experiencing the same issue. The person who originally posted their problem confirmed it was a torque converter and attached an image of the GM TSB (which I have attached).
http://ls1tech.com/forums/gen-5-cam...6-shuddering-lower-speeds-light-throttle.html
Obviously I wouldn't be spending the time or energy to research this, write these emails, bring my car in, etc. if I didn't feel strongly that this was an issue but I understand that I am not a mechanic. Hopefully you and your team can recreate the problem and this will be resolved.
Again, thank you for taking the time to take a ride with me, read this email, and address my concerns. I just looked at my calendar and I'm actually dropping the car off Wednesday night for service on Thursday morning.