I have a FFV 3.0 2X4 2000 Ranger that has about 60,000 miles on it. A few months ago it started to miss/stumble at around 2,000 rpm. I pulled the engine codes once the CEL came on and the codes P1151 & P1131 were revealed pointing to a lean misfire. I started out by changing the 02 sensor and this didn't help. After reading in my manual and posting some questions online it became apparent that the DPFE sensor could be the problem. I replaced the DPFE sensor and it completely cured the problem!
I am just posting this in case anyone else has the same problem and perhaps can later benefit from this info.
Could be that the bad DPFE was reading an open EGR valve even though it wasn't open.
Under those circumstances, the PCM would be reducing the fuel requirements based upon a faulty signal telling it that exhaust gases were being routed back into the combustion chambers, when in fact that was not happening. Reduced fuel injection time = lean condition.