stbd frame flex dilema opinions wanted

okay so I just got the bed all mounted up and noticed that when I air the truck up the rear of the bed moves up... the frame is flexing in front of the crossmember in the pictures, my question is what do you guys think the best way to strengthen the weak point would be? I already have to repaint the back half of the frame so I would like to limit the modifications to the back half only.. I don't want to have to repaint the whole frame
 
here is how the frame is layed out minus the gussets laying on the ground in front of the 4 link crossmember

this is the body lines when layed out kinda hard to see but they're pretty straight

here is the body line after I put air in the bags notice the how straight the blue chalkline is now
 

and this is how much the f#cker is moving

this is where the frame is flexing for sure

any opinions on how to fix this?

im no fabricator but id put a gusset on top of that joint to tie the 2 sections together...

this is what I was thinking about doing

this is what i was talkin about and i think it would be all that would need to be done...

I've seen Max mention that he runs rails from the top of that rear cross member to tranny cross member to help with that issue.

---------------------------------------------Originally posted by draggin95nissthis is what i was talkin about and i think it would be all that would need to be done...---------------------------------------------I thought of this as well but I just didn't think it would be strong enough... guess I should have mentioned that the track has a tilt bed and the 300lbs+ bed is mounted by two points on the very rear of the frame, which puts more than your average amount of stress on the framethe front just mounts to the cab

---------------------------------------------Originally posted by KAOSSI've seen Max mention that he runs rails from the top of that rear cross member to tranny cross member to help with that issue.---------------------------------------------yeah unfortunately I don't think I have enough room for that between the crossmember and the cab... basicly what max is doing is adding some triangulation from the front of the cab to the back of the cab... that's kinda what I was getting at with this only not as long of a triangle as max mentioned

---------------------------------------------Originally posted by SlammedStrollerthis is what I was thinking about doing---------------------------------------------im not all to sure that would work you would just be tieing in the rear of the frame to the crossmember and the crossmember is after your flex point in my opinion...maybe doesnt look like the tubing in the forward half of your frame is doing much good because of the way you have it laid down yourr losing alot of strenght.

well the 1st thing i see that might cause a problem is that you have the 2x3 laying down under cab and then its standing up for the backhalf, it will work but you have to plate both sides and top. so what i would do is get a piece made or make one yourself that is 2x3 on one end and 3x2 on the other so it fits boths pieces flush, then make you a gusset that fits on the outside. if i could draw id show you

---------------------------------------------Originally posted by jucieddime00---------------------------------------------Originally posted by SlammedStrollerthis is what I was thinking about doing---------------------------------------------im not all to sure that would work you would just be tieing in the rear of the frame to the crossmember and the crossmember is after your flex point in my opinion...maybe doesnt look like the tubing in the forward half of your frame is doing much good because of the way you have it laid down yourr losing alot of strenght.your right bro but if you look in the red circle I drew a bigass gusset in black---------------------------------------------