Classic/Antique Car Repair: 1970 Chevy C/10 leans to the left, chevy c, center bottom

Question
Hello.   My 1970 C/10 - CST body leans to the left.  I measure on level ground each side from the ground up to the center bottom of the arch of the fender and it's an 1 1/2" lower on the left side.  Truck has air bags with 2 switches -- 1 controls both front and 1 controls both rear.  Any reason in your opinion why it leans?

Answer
Ok, how about a little more information. I take it that the springs have been removed and that the air bags are the only suspension, is that right? What is on the truck for shocks? Were the air bags installed on the factory mounts or were new mounts made for the air bags? Are there leveling valves in the system? has the body and or frame been altered? Get back to me and we will go from there.
Brad