1987 Dodge Dakota 3.9L v6 4x4. When accelerating, engine quits and sputters as soon 60-65km/h is reached

Check if your distributor has any slop. Turn the rotor inside and feel how much play there is. If there is play, then I would be willing to bet that the "gear" on the end of the camshaft may need to be replaced. I am having a similar issue with my 87 Dakota 3.9 4WD. I haven't had a chance to put a new distributor yet, nor do I know if I will. The way dodge setup the end of the distributor is nice if the distributor gaskets are worn out, but unfortunately the gear on the camshaft has been known to wear out and need more intensive work to repair it. If it is the end of the cam, you will have to replace the gear. Basically what happens is the timing is going to be jumping back and forth a couple degrees and it will cause the engine to be igniting the mixture too soon or too late, or every once in a while just on time. Also check the idle control solenoid and see if it is sticking, that can give you an inaccurate reading on the harmonic balancer when adjusting your ignition timing. This will cause you to incorrectly set your timing and will definitely cause a constant lack of power.