2020 silverado, double cab, 5.3L 8L90 8 speed transmission. I have a vibration issue also. It started with 4 miles on it and still does it with 11,000+. Using a "easy" foot on the brake it is not noticeable. However, if you have to be a little aggressive on the brake, coming out of high gear, the truck starts to vibrate around 40mph as you slow down, it stops 20-24mph. Lots of complaints online about this also, and yes, no help from GM or the dealer, yet...truck is there now being looked at again for the 3rd time. I drove another truck at a different dealership, same problem. The vibration can be heard and felt in the seat and steering wheel. From time to time I also get a hard shift from 1st to 2nd.
It appears the TCM is not letting the transmission downshift. However, I was hauling some material the other week which added about 500 lbs and experienced no vibration. Unloaded truck, test drove and the vibration returned. Loaded truck, test drove and no vibration. Also, it you shift into neutral, you don't get the vibration.
Consensus......the TCM is programmed to stay in a higher gear as long as possible, (fuel efficiency efforts) thus the vibration before the downshift.....add the weight and the TCM senses this and down shifts....
Depending on your transmission there is a lawsuit against GM.....the 8L90 and 8L45 are listed in the suit.
2020 silverado, double cab, 5.3L 8L90 8 speed transmission. I have a vibration issue also. It started with 4 miles on it and still does it with 11,000+. Using a "easy" foot on the brake it is not noticeable. However, if you have to be a little aggressive on the brake, coming out of high gear, the truck starts to vibrate around 40mph as you slow down, it stops 20-24mph. Lots of complaints online about this also, and yes, no help from GM or the dealer, yet...truck is there now being looked at again for the 3rd time. I drove another truck at a different dealership, same problem. The vibration can be heard and felt in the seat and steering wheel. From time to time I also get a hard shift from 1st to 2nd. It appears the TCM is not letting the transmission downshift. However, I was hauling some material the other week which added about 500 lbs and experienced no vibration. Unloaded truck, test drove and the vibration returned. Loaded truck, test drove and no vibration. Also, it you shift into neutral, you don't get the vibration. Consensus......the TCM is programmed to stay in a higher gear as long as possible, (fuel efficiency efforts) thus the vibration before the downshift.....add the weight and the TCM senses this and down shifts.... Depending on your transmission there is a lawsuit against GM.....the 8L90 and 8L45 are listed in the suit.