Why does your 2005 lesabre shift smooth when cold but shifts hard when warmed up?

A 2005 LeSabre may shift smoothly when cold but experience hard shifts when warmed up due to several factors, including low Transmission Fluid levels, worn transmission components, or a malfunctioning valve body. As the transmission fluid warms, it can thin out, potentially exacerbating existing issues or revealing underlying problems, such as a failing solenoid or clutch. Additionally, overheating can lead to fluid breakdown, reducing its effectiveness in lubricating and facilitating smooth shifts. It's advisable to have the transmission inspected for any faults or necessary fluid changes.