I have a 1998 Dodge Dakota 3.9 V6 that I bought used in July 2014 with about 148K miles. About two years ago, it started to intermittently sputter, backfire, hesitate and sometimes shutoff. This would happen sometimes at takeoff and even driving at various speeds. I thought it was that I not done a proper tune-up, so I took it to a shop for a tune-up, and to another shop for a diagnosis after that.

I don't think I have put more than 7K miles on the truck in the time I have had it. I have replaced the throttle position sensor, idle air control valve, pickup coil, fuel injectors, and about a month ago, added an inline fuel filter. (I know, the fuel filter is located inside the tank.) Adding the fuel filter made it run fine for about two weeks, then the problem returned. I have also added fuel injector cleaner when I have filled the truck, and it responded well to that for a time. But it has always returned to the sputter, backfire, hesitation.

 

Unplug the front O2 sensor. See if it runs any better. if it doesn't, may be a failing crank sensor.