You may be able to temporarily remove the front driveshaft and road test it.
Mark the front and rear flanges so it goes in the same way it came out. Any drivetrain fault codes?
The decel sensation may be a program characteristic of the ETC.
If you are still under the 3/36 warranty, I would get it documented on a dealer repair order and have them diagnose it. You want the latest and greatest PCM/TCM/TCCM (transfer case) software updates installed.
We took it in but because there were no fault cods they wouldn't touch the car and the sales rep said it was nothing they can do. but everytime you left of gas pedal you get like a squeaking noise and its applying the brakes like how it does with the acc.
Not everything will set a fault code. You need to speak with service, not sales.
A repair order has to be written and signed and a tech needs to drive the car to verify the concern.
If the service advisor can't help you, go to the service manager.
There is a problem with the car. You may get a mild decel sensation like the brakes are on, but it shouldn't be a strong decel and the squeak certainly isn't normal.
If it can do it on a lift, then the tech may be able to locate the issue.
Why are they declining to service the car?