The UI.
I wish the user interface for upgrading & tuning was much more consolidated.
It’s diced into bits-&-pieces spread across a lot of screens & tabs, making it bothersome to view & navigate.
I also wish there was an info card/tab on each car’s details in my garage (and/or in the tuning menus) showing a consolidated parts list of what’s on the car’s current tune without requiring me to navigate into the upgrade shop & tab across all the sub-categories of parts.
It’s the same old, recycled, slow, clunky UI that it’s always been. No evolution. No thought seems to have ever been put into streamlining the workflow for tuners.