Today I had the front rotors and brakes both sides as well as the right side U-Joint replaced. I'm still experiencing a shimmy/vibration at about 20 MPH down to a stop. What else could be causing this?? Motor mount? Something goofy with the computer and the breaks pulsing??

It is unclear from your description if the vibration you are experiencing is through the brake pedal when you are braking or in the front suspension generally. So I assume you are feeling the vibration through the brake pedal when braking (pulsations) and that what you are describing is brake shudder.

There should be no brake shudder at any speed if the front rotors and the pads are new. However if the rotors are not perfectly seated on the hubs there will be a poor alignment between the brake caliper and the rotors and you may get brake shudder when braking . If this is the problem in my view the only way to fix it is to remove the rotors, clean up the hub area and re-seat the rotors.

Also the wheels need to be bolted to the hubs in the correct sequence and with the correct torque setting on each wheel nut.

I might also do a front wheel bearing check on the vehicle. It is unclear from your description if the vibration you are experiencing is through the brake pedal when you are braking or in the front suspension generally. So I assume you are feeling the vibration through the brake pedal when braking (pulsations) and that what you are describing is brake shudder. There should be no brake shudder at any speed if the front rotors and the pads are new. However if the rotors are not perfectly seated on the hubs there will be a poor alignment between the brake caliper and the rotors and you may get brake shudder when braking . If this is the problem in my view the only way to fix it is to remove the rotors, clean up the hub area and re-seat the rotors. Also the wheels need to be bolted to the hubs in the correct sequence and with the correct torque setting on each wheel nut. I might also do a front wheel bearing check on the vehicle.