I've noticed both of these problems, which started with less than 500 miles on the car. (2015 3.6L LTZ) The weird shifting on deceleration/coasting is more of a minor annoyance for me than an actual concern. Here's the post I just submitted to CarComplaints.com | Car Problems, Car Complaints, & Repair/Recall Information
. Mine may not be live on the site yet, but there is one other complaint there for the same issue.
2015 Chevrolet Impala Hesitation: 1 Complaints
Post in case it's not yet live at the above link:
Bought the car brand-new. So many wonderful creature comforts and a powerful engine. I love nearly everything about it. I've been a Chevy guy my whole life (father worked for GM for 40 years), and I read all the glowing reviews from the car magazines and just knew I was buying the right car.
However, the transmission is an embarrassment to an otherwise near-perfect car. During the 1-2 and 2-3 shift, there is a significant delay between when one gear disengages and the next engages, resulting in a momentary loss of power/acceleration. This is particularly disconcerting when turning left across a lane of oncoming traffic. It feels like the car is going to stall. No other gear sequences seem to experience this same issue. I've tried the "manu-matic" shifting, and it has the same issue. Click the "+" to up-shift from 1-2 or 2-3, and there is a delay between disengaging one gear and re-engaging the next.
I'm no transmission expert, but it feels like one of two things to me: 1) There is a software issue that is attempting to make the shift feel "smooth" by inserting a hesitation into low-speed shifting, or 2) There is a design issue or manufacturing flaw that is not providing enough fluid pressure at lower RPMs to ensure crisp shifting.
I've had it in to the dealer twice for this issue, and they are unable to provide a solution. I've test-driven another 3.6L LTZ from the lot, and it had the same issue, so it appears to be a transmission design or software issue, and not an isolated problem with my car. I first brought it in for this issue with about 500 miles on the car. They were "unable to duplicate the concern", and suggested I wait until about 200 miles on the car to ensure the PCM had sufficient time to "learn". Well, I've got nearly 9000 miles on it now, and still the exact same problem.
The question I keep asking myself is, "How did this POS transmission not get absolutely destroyed by the C&D, Motortrend, etc. reviews?" I can't find a single review online mentioning the poor transmission. Chevy either gave them different transmission software, or this is a 2015 issue and the 2014s were unaffected. No way a pro vehicle reviewer doesn't pick up on this.
As much as I love everything else, I wish I had never bought this car. Friends and co-workers ask how I like it, and I have to tell them I don't because of the transmission. To not be proud of the beautiful, comfortable vehicle in my driveway because of a lousy transmission... This is not the kind of experience a new-car buyer should have.