Is this EBCM or bad caliper?
 

2001 Silverado, replaced rear brakes and one side was OK but pass. side was worn so bad it had to have a new rotor. After driving about 100 mi. I am noticing rusty specs forming on the wheel and it gets awfully hot you can smell it and see smoke come from it. Today at highway speed it started shaking as though the ABS was kicking in, I have also noticed a rapid surging effect when braking for quite some time along with ABS lights on. Could a bad caliper cause this or is it more likely electronic?

Thanks

You probably want to get it scanned for what the ABS indicator is about. That'll get you closer to the correct diagnosis. Mind, most hobbyist scan tools won't read ABS trouble codes.