If you were to be a little more discriptive about what you feel when saying not grabbing.
On wet pavement how does the ABS kick in?
When you pressed the piston back into the caliper, you had the top off the brake reservoir, did you check brake fluid level? too much fluid?
If you did the guide pin bolts to around 15lbf by just feel that should be sufficient.

Had you opened the bleeder nubs at any of the calipers?

what make were the rotors and pads?

with the car turned off, when you pump up the brake pedal to make it firm, what happens when keeping your foot depressed when you turn on the engine?

And how did you press the piston back into the caliper? the piston rubber seals weren't deformed?

just trying to hit everything that coud be wrong