Before you change anything else out measure the flats on both drive shafts, and the slot in the oil pump driven shaft, there appears to be quite a variance there. Somethings not right....

 

You see? New does not always mean good. Even new puppies die at birth.

 

Months ago I installed a crankshaft sensor on my 2000 Jeep Grand Cherokee, but it didn't come with a paper spacer. I recently changed my fuel injectors and there were no codes, they cleared automatically. Recently my scan tool comes up with P1391 could this be that the spacer is missing?

 

You do realize that NAPA does not manufacture those parts right? The oil pumps NAPA sells are manufactured by Sealed Power which is a pretty reputable company. I have had more OEM parts fail over the years than aftermarket parts. You did not state what weight oil you are running but a thicker viscosity oil will generate a higher load on the pump drive shaft. Bottom line is that SH*T happens and sometimes there is nothing you can do to guarantee you will not have a problem. Glad you found the problem and that it did not cause a total engine failure!

 

All I'm going to say is I had a brand new Melling pump shear it's shaft after 1200 miles. Melling is Mopar's OEM. It appears improper heat treat was to blame. The broken edges of the tangs were very crystalline in appearance.