i have an 03 chevy silverado 1500 z71 4WD. pretty much stock all around. i'm not to happy with the way it acts when im off road (nothing major mainly bumpy hunting roads etc.) i also haul a 14' trailer. when i use that trailer my truck sags terribly. i know its not to much weight cause my friend hauled the same trailer and there was some sag but not near as much as mine and he has a base model siverado. ive been looking around at different brand and they all have different fit applications (for my year model) for the same shock. ive been looking at bilsteins 5100 series and rancho 7000 series and 9000 series. i liked the 9000 series cause they are adjustable. my question is has anyone used these shocks on the same truck as mine? or will some fit? also do i need a leveling kit or anything? any help would be much appreciated!!