I, likewise, had a hell of a time with removing the shift knob when I had to replace a torn shift boot. Pulled the entire shift assembly out of the car. After pounding on it for days, with no luck, I ended up taking a piece of copper tubing (about an inch long), with an inside diameter the same size as the shift shaft. I split the tubing longitudnly, opened the split tube enough to fit around the shaft, and then reformed the tube as close as possible around the shaft. I was able to pound this tubing up towards the "locking fingers" of the plastic retainers, which lifted them, just enough, out of their grooves, which released their grip just enough to allow me to pull the knob off the shaft.