I would say the 60mph shake would be your tires or rims.
And who ever said your motor mounts were causing this, I'd never take it to them to work on
It wouldnt hurt to get your cooling system flushed.
Rust occures when not enough coolant was used, like just using striaght rusty tap water.
I use filtered/bottled water in my cooling systems, this keeps iron and other contaminates from poluting the ssytem.
Hope that helps !