Leaning vehicle

[crabcake]

I have a 2013 GMC 1500 Serria 4x4 that I bought new.  I had a local alignment shop install a 3.5 inch Rough Country lift kit but only on the front shortly after I bought it.  I installed Firestone air bags a few years ago but never put air in them. The front lift kit raised the front a little higher than the back.  The air bags lifted the rear end a little to make it pretty close to level.   So, sometime back, its hard to say when, I noticed at a distance from the front of the vehicle, it looked like it was leaning on the driver's side.  A level proved that, and it's just over a half inch front and back.  I am being told there is not much to do, maybe change the front strut but that doesn't guarantee any fix.  I would like to know if anyone else has had this issue and what did they do about it?  The alignment shop told me this is normal with all chevy's and gmc trucks.  

[CamGTP]

It is normal because the fuel tank is on the drivers side.

[swathdiver]

It's normal.  You sitting in the seat all the time didn't help either!  When I replaced my front springs, one of them was an intsy bit taller than the other but after two months it didn't make a difference.  1/4 different side to side up front and 1/16 side to side out back.  Turn the radio up...