It certainly helps that you've done a PCM scan and found only the P0300 code. While not eliminating other causes, it reduces the possibilities.
Since the misfire episodes are limited to a small RPM range, I think we can find the problem in one of two places.
If you find nothing wrong with your plug wires, I would expect this to be the next-most logical spot to look.
The correct index procedure is a bit drawn-out and I hesitate to list the whole thing without knowing whether this is needed. While the index can be carried out with the use of the factory scan tool to within a single degree, the actual real-world adjustment for satisfactory operation is somewhat less demanding.
So, if you find this is the path you need to take, let me know and I'll send you information to allow an accurate method of index for your distributor.
I'll leave the light on.
Will do, J.
Off to work for now. Thanks.
Long day, but it sure is beautiful this time of year. Hope your day was just as nice.
Distributor index goes something like this. I'll actually plagiarize an earlier Chrysler TSB and insert my own cautions as required. Remember that this procedure places the distributor (and the cam sensor within) to an operating medium with the crank sensor. The variance allowance is fairly large, something in the neighborhood of 12 degrees, either before or after the crank signal. That's pretty large. I hope we can put the index closer to the ideal zero degrees, but that can only be confirmed with a factory scan tool. I'll include my tips in italics.
Either way, you should be within a few degrees of perfection... easily enough to prove or disprove my theory.
Loosening the distributor may be the biggest obstacle. It's not easily accessed.
But be careful to first position the engine (no backing up!) to the V8 mark on the crank balancer. There is also a V6 mark, but it isn't anywhere near the TDC mark on your balancer. Don't be fooled. Clean the balancer marks if needed and set the engine position using the V8 mark at the timing cover TDC mark.
Then, you can either use the 5v-0v-5v transition point by turning the distributor (works) or my method of backing the distributor considerably past the switch point and then rotating the (CCW) back until the sensor switches (as identified by DVOM or relay click). Either works.
J, make sure and let me know how this comes out. I mean it. Distributor index problems aren't common anymore, but it can still happen. I use modeling for my diagnoses, where it might or might not pan out. If we need to go forward, it's all good.
I'll be here. Remember the light's on.
One last thing. If you'd like to read the original TSB from which I paraphrased this post, type in Dodge TSB 18-08-93 into your search engine. The original TSB involved replacing parts your truck won't require.