Rear end "shifting" under deceleration on sweeping turns

[heitzke]

Title is the best way I can describe it. I DID read through a very long thread on a very similar sounding topic but didn't really leave with any sort of resolution or further thoughts on the subject.

The car is a '15 base model without any sort of adaptive suspension. The only change/variable that i've added recently was getting the GTS steering/diff/mdm coding from Kubax86 on here.

Obviously the vehicle coding seems to be the issue here but I'd like to really understand what's going on here.

Scenario: longer sweeping turns, like curving entrance ramps and decelerating in the 30-40mph range the rear end feels like it's... shifting hard from one side to the other like it's trying to determine how to set the car up through the turn.

At speeds any higher than this and through accelerating (even lightly) it feels totally fine and stable.

Variables: The only thing that changed was the coding, which besides this oddity I really really enjoy. The car feels more planted through higher speed turns, putting down power and overall steering feel. That being said, I don't really want to code back to what the base '15 felt like.

Other related bits:Tire pressure was 3lbs less on one side, alignment was done about a month ago and was totally fine.

Next steps: I did reach out to Kubax86 about it, but in lieu of that I think i'll try the same entrance ramp in various MDM/ESC off settings to try to pinpoint if it's MDM or differential coding related.

I surely could just accept it for what it is and just have a weird handling quirk, and/or just not take entrance ramps like that, but where's the fun in that? Let's over analyze everything.