We traded our AWD Rendezvous for a car which is has 4WD, but 4WD doesn’t always kick in when we need it in the winter. Can’t get up our driveway when it’s slippery because it stays in rear wheel drive. Never had a problem with the Rendezvous–in fact, front wheel drive vehicles have a better chance of getting up the drive (long rocked driveway, with a hill at the beginning). Maybe I have to gun it at the bottom of the hill to get 4WD to kick in? Maybe the car’s 4WD isn’t what we thought we were buying (STS4).
Your Caddy also has AWD (not 4WD, which is found mostly on trucks), but a different type, which might not engage as quickly. It also may be caused by the STS having tires less suited for snow than the Rendezvous.
The AWD system in a Caddy uses a center differential which means it is little better than a 2WD vehicle when trying to climb slick driveways. Some SUV’s with AWD have a handy “lock” switch which sometimes works to provide 4WD traction…