I'm going to reply to your post here, Doc, since it has to do with the vehicle in
this thread.
I guess I missed something.
What’s up with the transmission?
The torque convertor is acting up. It's a known issue on the 8 speed autos and affects the Camaros, Corvettes, some Cadillac models, and the Silverados / Sierras that use the A8.
Cruising along on flat ground or especially on a slight hill, trying to maintain speed but not gain speed, the torque convertor "pulses" as it locks-up and unlocks. It feels like running over rumble strips every 3-5 seconds or so.
That can get
very freakin' annoying, especially on a road trip. I actually cut the NM/AZ/UT trip a day or two short, just so I could get back home and get out of the car with that "shuddering" (that's what they call it on the Vette and Camaro forums) transmission.
I drove nearly 800 miles that last day, just to get back home and not have to deal with that transmission another day.
I've had it in the shop once. Step one of the TSB is to do a triple flush on the transmission. Step two, after giving it back to the customer, claiming it's fixed, having them drive it at least 200 miles, and them
still complaining about the issue, is to replace the torque convertor and update the transmission tune.
The "fix" I have heard on
the forums is to adjust the tune so that the TC engages at 100% when it is
supposed to be engaged. Of course, tuning the transmission voids the warranty and GM's "updated" tune does NOT have 100% engagement of the TC.
The ZL1 with the 10 speed is not effected by this. Of course, neither is the manual.