Tim,
What I have done in the past is to grab the metal neck of the cable (just behind the nut holding the cable to the dashboard - but not on the threads) and then using a wrench to work the nut back and forth. Eventually, it will come loose for you. You said that you have been soaking it with PB blaster for a long time. Be patient.
Once the cable is out - you can try to hit the cable on the concrete to loosen it up. Just as long as it is not wet with lubricants.
I will then pull the cable out of the housing, clean up the cable, and blow it and the housing out with air. You don't want to use lubricants that will get the rust sticky. If anything, use dry graphite. The cable will go back in the housing. This works for me.
I hope this helps. And you get the cable off.
Best of luck
