New to 6.7 power

[charles P Harp]

just got a 2013 6.7 3500 dually and have vibrations at about 75 mph or so. Just had all three universal joints replaced and balanced.
I noticed today in the grass both tires spend not one then the other, at the same time. Is that right or has someone change it.

 

[crash68]

Chances are the truck probably has a limited slip differential.
Although a CTD dually in 2WD can turn into a Sit-N-Spin when traction is low like on snow, grass, etc. The combination of being really nose heavy and the rear weight spread over double the tire area makes it easier for the rear tires to spin.
As for the vibration you may need to have the tires road force balanced.

 

[charles P Harp]

I did a test on concrete and I can hear the driver side loose grip on sharp left hand turns. If I lift the rear end up and hand turn the wheel what should I see.

 

[mtnrider]

You could try plugging you VIN into one of the window sticker lookup sites and see what it came with from the factory?

Here is one..

https://windowstickerlookup.com/




.

 

[BubbaJo]

looks to me you have a posi rear end. Which is good when the weather gets bad. as for the vibration try going in and getting the tires rotated and balanced.