the shocks will self level themselves after driving for a mile or so.
to check if your pump is working locate the height sensor in the left rear wheel well. disconnect the rod on the control arm end. gently push it up. in about 5 seconds with the car running the pump should activate. if that happens and the car does not start to raise it'* rear then your air shocks are toast. if the compressor does not come on look in the rear fuse panel under the back seat for the ELC relay and the fuse for it as well. replace and repeat the test
2005 Pontiac Bonneville GXP
2008 Chevy Impala 3LT 3.9L (9C3)
2000 SSXP (retired) all over the country in a million pieces