89 Camaro Transmission Clunk

I just picked up this car, I got it because of the condition of the body, not the mechanical condition.
Unfortunately it has a problem that I can’t seem to find the awful clunking noise it is making. It really slams, the whole car jumps, when you are on pavement and you hit the gas hard, or when your accelerating fast, and it shifts. If you’re on lose stones, the tires break lose and it doesn’t make the noise.
I originally was thing U joints, so I changes them, and also changed the seal in the differential, put new oil in the diff, and checked that all out, and everything appeared find. There is plenty of fluid in the trans, and the flywheel bolts appear to be tight also. Motor mounts are also fine. The car does seem to accelerate slowly too, I think that might just be a plugged cat converter. Anyone have any Ideas?

Could be the torque arm mount has broken. Mines toasted and it does the same thing when shifting into 2nd gear.

Well the problem is hopefully solved, we put a jack on the trans to see if it would move, like the torque bar was broke, and a problem was found, the transmission mount was broke, I’ll probably get the new one in it tomorrow, thanks for the idea

check differential and tranny mounts

Well the problem is hopefully solved, we put a jack on the trans to see if it would move, like the torque bar was broke, and a problem was found, the transmission mount was broke, I’ll probably get the new one in it tomorrow, thanks for the idea
that would definately be clunking