Pinging/knocking(pre-ignition) is fairly common on the 3.0l, but not normal.
I would look closely at the EGR system.
It has 3 parts.
EGR valve, vacuum controlled valve, it opens to allow exhaust gases into intake, this cools cylinders when under load, yes, sounds odd but that is why it is there
Cooler cylinders means no pinging.
EGR Valve ONLY OPENS after engine is warmed up and when engine is under load at higher RPMs.
DPFE sensor, this tells the computer if EGR valve is open and by how much.
EGR Modulator/Solenoid, this is a 12volt vacuum valve, computer pulses 12volts to this device to send vacuum to EGR valve to open it.
EGR valve opening at low RPMs will cause misfires
EGR valve not opening under load will cause pinging.
Other things to look at would be general engine wiring.
Have engine warmed up and idling then start moving wires around, see if you can duplicate the misfires on bumpy road.
Last edited by RonD; 01-02-2015 at 12:15 PM.