I had a very similar issue with my 92 Dakota.

After months of frustration, checking codes, checking wires, changing parts, I stumbled upon an old TSB for the bronze bushing the oil pump drive shaft rides in.

Seems the early Magnums has a bad batch of bushings, and they would wear, allowing the distributor shaft and timing to fluctuate. If the timing gets too far out, the CPS doesn't get the correct signal, and it triggers the ASD relay.

I replaced the oil pump intermediate shaft, and bushing, and have had 6 years of dependable service from the old Dakota.

I had none of the surging, or noises, the TSB mentions, but my bushing was extremely warn, even the teeth on the drive gear had a knife like edge ground down when compared to the new drive gear.

Check the diagnosis section in the TSB, its an easy test with twisting the rotor.

http://dodgeram.info/tsb/1993/18-08-93.htm