I had trouble getting an initial good pedal in my Spyder when I installed the 4 piston fronts and single piston rears with the correct MC. I even used Teflon/SS braided lines. I did not have to resort to residual pressure valves or anything like that.
When bleeding, you need 3 hard and rapid pumps and a hold, then bleed. Pump that pedal VIOLENTLY and quickly. You'll be amazed at how much air comes out. You should be good after that with a nice high and firm pedal.
You owe me a beer next year, Alan...