Get under your car and make sure the sensors are zip-tied at a 90 degree angel (all of them), parallel to the ground - this should prevent the compressor from kicking in. You should also make sure the hoses are plugged (where they would normally attach to the air springs) so that no air comes out if/when the compressor kicks in.

That should solve your sensor and warning issues.

As for 'driving like a tank', like any vehicle, there are a number of different springs that can be used. The amount of tension (compressability) on the spring controls ride comfort. If you dont like your current springs, search for something softer that may provide the 'boaty' feeling you are probably used to.

 

Thanks for the input. As of this morning the mechanic that did my conversion completely killed my car. I don’t know if they put the wrong coil overs in or what. Car felt low and stiff on ride, drove for about 5 miles and the car went crazy. No brakes, won’t stop in park, loud metal on meta grinding sound. Wont go into gear all of a sudden, smoke coming out back left wheel well and loud grinding in both front wheels. I had an occasional airmatic malfunction warning when I dropped it off to them. Paid $3300 for a coil over conversion - Now I have a completely worthless gl450 with fancy new coil over springs.