Highway vibration

[Jcp21]

Looking for a looking advice on where to start looking for a solution.  2020 Sierra 1500at4….83,000 miles…5.3l. V-8

 

I have a fairly major vibration at times when driving….can be going straight and feel it….going up an overpass and feel it….when windy you can really feel it.  The best I can describe is like the engine bogs down, and gives a rumble noise and shake.  I can watch the tach move about 100-200 rpm when the noise/vibration stops.

 

I have new shocks (5100s in the front and fox 2.0 in the rear)

New tires - cooper at3 4s (my second set)

 

Noise/feeling was present before and after the shock and tire change

 

Could this be motor Mount? Need new spark plugs? Transmission fluid? Transfer case fluid?  
 

any help is greatly appreciated 

[CamGTP]

A part of me wants to say torque converter shudder, when it said the 100-200rpm bounce that is why it comes to mind.

 

When the problem is happening, if you take your foot off the throttle to coast does the vibration seem to go away?

[BlancoSilverado]

1 hour ago, CamGTP said:

A part of me wants to say torque converter shudder, when it said the 100-200rpm bounce that is why it comes to mind.

 

When the problem is happening, if you take your foot off the throttle to coast does the vibration seem to go away?

I agree, now the 10-speed is still too new to know if they're going to have issues like this, but, it sounds like the same issue the plagued the 8-speed trans. Are you still in warranty (assuming not)?

[Jcp21]

Out of warranty, and yes if I take pressure off the gas or even pressure on the gas it goes away.

 

Reminds me of the old v4 to v8 cylinder switch as in previous models

 

also have a very slight vibration at idle

[kmeleon]

But you never noticed this before? You could shift to L7 or L9 (if it's a 10spd) and see if it goes away. That will shut off dfm. 

[Jcp21]

Noticed for a while….try to ignore LOL

 

I have  used the L9 trick before.  I would say it helps, but not eliminate 

 

[4threeking]

I have the same exact issue. 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 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.

[silveradosid]

are you sure you have that correct, when installing lift blocks you increase the angle, putting the shims in the way you suggested would increase it even more