My G-Force Sports were super grabby. Maybe the rear end lifted off the ground!

OK, maybe not.
You may need to let the brakes settle in a bit. You said they were new, but didn't mention how recently the rotors/pads were installed. I also read in a recent post that the brake system is set up in a dual-diagonal configuration - great idea, actually. If pressures in the system aren't quite balanced things may feel a bit squirrel-y under hard braking. Be a great time to fully bleed the system and get totally fresh fluid in there ... I bet that'll help tons.