Lopsided

One of the trucks that i work on blowout a air bag its a 97 Freightliner single axle tank wagon. They put a new one on it and found that something else was wrong so i was called. It had a broken ubolt so i put both in and a new spring center bolt. They needed it so when the tools were picked up it was in use. They noticed it didnt set level. There is 3/4" differents being that the side i worked on is lower. I replaced the bag on the other side it was a different brand. I let the bags down and this side the axle and frame stops touch and the other side is 3/4" apart and when you run the gaped side up on a 6x6 it dosent touch.The other side it had a broken spring when they got it about 60 days ago that i replaced and it sat level or close to it then. The front axle is almost level with the frame maybe a 1/4" differents.I looked the frame over very close and it look ok but with the tank and every thing its hard to tell if its strait.I dont like this truck alot because it looks like it started as a tractor some time ago i think and has a single frame.Any Ideals i thought about replaceing the blown air bag side spring because it was under a bad twist when the ubolt broke? The Ubolts were rusted bad were they run through the axle plate.