p30 stumble problems/ fuel pressure regulators

you Won't believe this, getting mis-fires again, then the upstream bosch sensors started reading low????? one has completely failed. Huh???? Not even 6 month old...... I replaced both upstream sensors with AC Delco's as I did the down stream units and all is well again, no-misfires, wow I'm really surprised at these thing failing. Auto zone stood behind their warranty and refunded for the bosch units. What a great company to do business with.