SVXY Shakes, Rattles, but Rolls

[LarryIII]

I have a problem with my '92 SVX named SVXY.
When I step on the brakes at speed (above 50 mph) there are violent pulsations that shake the brake pedal, steering wheel the whole car and me the driver. It gets more pronounced when the brake fluid is warmed up. There is also a slight vibration when driving without applying the brakes.
To combat this problem the following has been done:
1) All brake rotors were ground smooth. The fluid was completely drained and refilled with fresh fluid and the brakes bled. None of the caliper pistons are sticking.
2) Got 4 new tires (Toyo Proxes 4, John), which were mounted and balanced.

The car does not pull to one side or other when running or braking, so I don't think it's an alignment problem. Since this problem arose, I noticed that my gas milage has dropped slightly. It has gone from 22 mpg to 20 mpg. I think that there is a slight brake pad rubing problem but have not found it yet and there is no excessive brake dust on the wheels, or "hot brake smell'. I run OEM brake pads.

Can some of you technical wizzards (like Tom & Tom) help?

Thanks.