May want to read through this thread for info on the LTZ suspension :
http://www.chevyavalanchefanclub.com/cafcna/index.php/topic,131766.msg1973986.html#msg1973986
Also when you listened for the leveling was the key in the ignition or did you start AV with remote start? Also obvious but someone will ask, did it level off at all even if it took a few minutes and you just couldn't hear it? Then what is the tongue weight of your boat trailer?