Mark has it right, Dave. Bleeding sequence is important. Any air between the rear master and the front calipers may defeat the Delay Valve.
Correct bleed sequence for Your 99, FirstPeke's 2000, and my 2001 are all the same. ABS II. Here 'tis, per the 2001 shop manual:
Lever (front) brake line
Open top bleed valve on either side and bleed. (I use a Mity Vac.)
Open top bleed valve on other side and bleed.
Pedal (rear) brake line (here's where sequence gets important)
Left front caliper lower bleed valve
Right front caliper lower bleed valve
Rear caliper front bleed valve
Rear caliper rear bleed valve
(Suck a bunch of fluid thru all the lines. Book says 1/2 liter total in the system!)
If that don't solve your problem, suspect the Delay Valve (not the PCV, Proportional Control Valve. I had it wrong in my PM back to you.)
Phil's diagram is correct:
The Delay Valve is the unlabeled component at the upper-left, between the Rear Master and the front calipers.
The PCV is between the SCM (Secondary Master Cylinder) and the Rear Modulator.
Given that your rear center operates correctly, but the front centers do not, eleminates the rear master cylinder.
In your postion, I'd first do another complete bleed, following the steps listed above.
Keep us poSTed.