Frame Ajustments for Bagged B2k

I just got this 1986 mazda b2000 it's got airbags in the front and air shocks in the rear. When i first got the truck i noticed that right where the cab meets the bed, it looks like theres an arch in the frame. And over the last few months it looks like it's gotten worse. If anybody could help me out with this little problem just let me know. Thanks