Has anyone had an issue with their 99-02 GMC/Chev 1/2 ton 4X4s with a bad sway in the rear end?

My truck was rear ended a couple of times. Once by a metro, again by a caddillac. It started after the metro hit me. The caddy made it worse.
The frame was bent behind the axle, and the dealership supposedly straightened it out and re-coated it.

When going over bumps the rear axle feels all wiggly.
If getting onto an expressway ramp say rolling around 40mph, Nail it, and the rear end sways violently side to side almost throwing the truck out of control.

When hot off of a light, it doesn't do it, but it feels like it's rolling from the torque.

Nothing looks bent, and the insurance man mechanic says everythings fine (Of course).

One thing I did change on the truck - I went from BFG KO's to Goodyear Triple Treads (These absolutely SUCK). With the BFG's the rear was wiggly but it didnt sway. Both brands were the same Size, 265 75R16.
Its got about 144K miles on it now.

Should I invest in an Addco rear sway bar?
Caltracs?

Any advice is appreciated!

 

Nobody has had this issue?

 

The only time my rear end sways side to side is when I nail it and I'm spinning.....

I think you could have some frame issues still.

Other concerns:
-You have big "bubbly" tires
-Shackle/leaf spring bushings worn?
-Loose bolts anywhere?
-Ever replaced the shocks????? Undampened springs can take a while to stop bouncing.

 

I have this issue sometimes and I have never had the truck wrecked. Mine, I believe is a result of running 34 inch tires on factory wheels. Prob should replace my bushings as well. Let me know if you figure it out.

 

265 75R16 Goodyear TripleTread Trash
Bushings could be worn - they are original
No loose bolts that I could see and all seemed tight.
Shocks were replaced with Gabriel HD shocks all the way around about 40K ago
My Rear Jounce bumper for the axle came up missing but I can't imagine that would cause it to sway violently. New one on order.

I'm wondering if I should purchase a rear sway bar for it.