Kenworth Frame bending

Hello everyone, I have a 1993 w900, the previous owner replaced the ag100 suspension with a 4 bag airglide from a freightlner due to rust issues. The original kw frame was kept just drilled a bunch of new holes for the new suspension, under the fifth wheel is rusty and thin. If you look down the frame from the back you can clearly see a slight bow under the fifth wheel, also the frame flange above the front set of air bags is bending upwards and the truck is riding very rough and feels very unstable ( loaded trailer seems to lean a lot more than it should). Another visible issue is that the angle steel that the fifth wheel plate bolts to is very wavy, visible bends between the bolts. Not sure if I need to replace rear frame rails or am I missing something. I have not found any cracks or holes in the frame or cross members. Any advice? Thanks a lot.

 

I uploaded a few photos. Not very good quality The bowing of th frame under the fifth wheel is very noticeable when loaded.

 

I have an ag100 cut off in very good shape that I will most likely put in but the frame is a different height so I did locate 2 nice 12' rails pre drilled for ag100 for $350. Prob my best bet and stretch 12" or so while at it.

 

They switched up the ears on the rear crossmember. Don't really think that should matter too much though.