My 2004 deville has been a jewel. I just noticed the transmission, instead of a smooth transition from drive 1 to two, I get a rough"slam"ingagement and the same each progressive upshift. However when I hit passing gear, there is a smooth downshift.
transmission shifting rough on 2004 Cadillac DeVille
The powertrain control module may have detected a fault and as a result has commanded full line pressure causing the hard shifting. The first step would be to check for stored fault code(s) in the powertrain control module. Any stored codes should be diagnosed and repaired and then the transmission operation rechecked. If you need someone to access and diagnose any stored fault codes, please use the following link to find a shop near you - http://repairpal.com/directory?address=24211&car_brand_names=Cadillac.