My 69 Ply 440 4 speed is doing something odd. when driving around 30 to 40 mph the car jerks back and forth, kind of like a weird power surge. it was not so bad last year but has got worse. I had the AVS carb rebuild last fall and the car ran great, so good in fact I got on it and broke a motor mount.

Put in new Mity mounts this spring, and it seems worse with the jerking, but I would not think that is my issue. after installing the new mounts, I drove it a bit hard and the power is not there that was there last fall. when I floored it it kind of bogged down and back fired just a little bit.

Any ideas what is going on ? Thanks