If you run in Manual mode and run in 7 for your 8spd, or 9 for your 10spd, the afm/dfm will not engage and the computer will not disengage cylinders as designed, to increase yur gas mileage, for whatever minor amount that is ! But if yu keep it from dropping cylinders, it might save you from known lifter damage that is known to result ! I went thru this with my 17 8spd model, and ended up getting rid of truck. I now have a 20 10spd 6.2, and have made the mentioned adjustments and still get 21-22 on hwy, 16-17 in town, and it runs on 8 cylinders all the time !
Good luck…

 

I actually contacted both companies that offer a tuner of sorts- Range Technology has a plug and play AFM disabled and Pulsar LT has a more extensive application that does multiple things aside from AFM disabling.

the issue is… neither company can give me a definitive answer if it works on the 2.7. Range Technology’s site says does not work on the 10 speeds and is for 6 and 8 cylinder, but no mention of the 2.7. Their representatives have me two different answers if it works. Pulsar LT on their site says AFM disabling on the one for the 8 cyl but doesn’t list it for the 4 cyl, but on YouTube people are commenting it worked on the 4 cylinder as well.

if you get one, let me know if it works!

 

go onto the gm authority website. join for free, then you can search for all the symptoms and reports about your model and engine . there are also gm 'official answers' on various problems reported in gm vehicles.

if it were me paying a dealer for successive $139. 'we found nothing' diagnosis charges, I'd demand that the dealer take your the issue and demand it be accelerated up the GM chain to reach the the GM tech engineers at HQ. write to Mary Barra the president herself. and see if you get some action. (check latest gm site for her real email. . . )

sign me -- an unhappy current GM chevy vortec 6.0 L 3500 owner , (now on our family's 13th GM vehicle since 1955. and it might be the last. )

 

I gotta say, mostly good overall, but these issues as discussed / revealed are not acceptable, especially when dealers service reps, in some cases deny finding actual causes for symptoms of problems that may lead to pending failures, sometimes that occur after warranty has expired, and you get the ‘sorry, your warranty has expired’ !

If my 20 model ever starts to have these issues, at the first sign of a potential problem, I will most likely go back to the F150, especially since it was rated best in crash tests against the other mfgs..

 

Finally got the time and an appointment that matched with my work schedule. Brought it in for the vibration and the service manager took it for a road test. Really great service at the dealership.

Brought the truck back and said he can feel the vibration and that there’s nothing indicating a mechanical problem. He said it’s like a small fish nibble on the end of the fishing rod. Said it’s just the way it’s built with the engine and transmission configuration. He said if gets any worse, bring it back in and they will look further into it. They made a service record for gm to see in the system. Haven’t even done the first oil change yet.

 

I had a 2016 Camaro with the A8, and it vibrated at around 55 mph. This was about 3 years ago because it was still under warranty. Apparently the A8 was designed for a very specific transmission fluid, and for production GM went a different route and the cars were plagued with the Chevy shake. They finally issued a service bulletin, drained and flushed, inspected for shavings, put in the right fluid, and the problem was gone. I have since bought a 2019 Silverado with the A8, and and I have been wondering if they had corrected the problem from the get go or not. I am guessing not as I get shakes and vibrations all the time. Feels like the transmission slipping, but I am guessing that it is this same problem. Anyone know if there is a bulletin out for the trucks as well?

 

11000 miles on my 2022 LTZ 5.3 8 speed. I thankfully do not have the shudder (knocking on wood). My 2015 C7 Corvette had the trans issues. It felt like you were running over speed bumps.

 

I have the same exact issue. the issue is the the driveshaft pinion. Chevy missed this somehow. Check your rear leaf springs and see if there is a shim, or factory lift block. If not try adding a shim, or buying a level with a tapered block.

If you guys want to keep the factory blocks just order 2.5 degree shims. This will angle the rear diff so the pinion on the drive shaft is inline with the transmission. Chevy should have these to begin with but I’ve seen some trucks have shims some don’t. This should be included but it took me forever to figure out the issue


https://amzn.to/3pbzmdj



Throw these on your rear leaf springs and point the narrow end towards the front and the thick end towards the back. that should fix the issue.

 

After 3 yrs and 31k miles, no issues with my 2020 6.2 10 spd.. I installed a Stillen Cold Air diverter up front under hood, and the larger cold air intake filter kit couple years ago.

I always drive in L9, which eliminates ‘cylinder shutdowns’ on highway, and ‘engine auto stop’ at lights. At normal speed limits 60-70, I am averaging 21-24 on day trips.

 

Any luck on finding the problem for the original post?