IN CASE ANYONE ELSE HAS THIS PROBLEM I SUSSED IT OUT !
So the Reshade requires you yo hit Shift F2 to adjust it - turms out that with GTA V, if you are using a 360 controller, and have a mouse connected, AND you open Reshade in game to adjust it, it screws up your controller.
So, adjust, and when happy, restart the game and do not open Reshade again. All is then good.
As for overly slidey car handling, I just took out the handling meta file and replaced it with the original.
All good, again.