My neighbor had exact same year Dakota as mine (1993) except his was standard cab with 3.9. I think he told me he was getting only 15 mpg too. Believe I heard others on this thread say the same thing. Doesn't make much sense to me.

 

Interesting.... So essentially just the the lower intake gaskets? my plugs didn't look fouled or anything when I pulled a couple of em but if the plenum has issues with that it couldn't hurt to replace to play it safe.

 

Yeah the guy I got mine from said he got 15 with mixed driving, and my first tank (which was mostly city driving) I got about the same. One thing I know for sure from following a couple TBI builds for chevys is that both chevy and dodge's TBI systems were verrrry temperamental to say the least. I know if you get them absolutely perfect and dialed you can get pretty decent MPG, sometimes even better than EPA numbers but if one thing is wrong the "house of cards" falls over pretty quick. Same with running issues as I am dealing with now haha

 

I did the Hughes Engines kit for my plenum. I have seen other post since that the gasket issue shouldn't be happening because of the alleged different expansion rates of the steel plate plenum and the Aluminum intake barrel. If that is so then the problem may be due to poorly installed gaskets at the factory. Anyway either way just do the gasket, or get a kit which adds in an alum plate and that issue is solved. I had to get one set of longer bolts with the kit, extra. I don't remember if the intake to block bolts needed to be longer too. If you do a kit they should be able to tell you.
I eventually put all new sensors in mine and even at one point just replaced all of the fuses just because it is old.

 

I did the math once upon a time, and the difference in expansion between the two was measured in ten-thousandths of an inch. Different metals ain't the problem, the bolt from the factory are too long, and the gasket compresses over time, then blow out, and leaks.

 

Well, in the end, I think I figured out the problem, though with all the changes, I'm not sure if it was a single point issue, or a cascade issue.

I've replaced the timing cam phaser, and the chain/gears while I was in there. I had to pull the timing cover off as the water jacket seal ruptured. Fortunately it did so towards the bolt and not towards the inside, so no water in the oil.

After reassembly the stuttering window narrowed a little bit. It also ran overall generally a little smoother, but still had stuttering and power loss when giving more than about 15% throttle. I had ordered a new VVT solenoid and I tossed that in there a few days ago. I drove it around yesterday and it was behaving a little better, and had more power lower end. It even went up hills and downshifted mostly correctly without loosing so much power it started slowing down.
Today I replaced the driver side knock sensor cable connection. Fired it up and within moments I could hear it already retuning itself. Took it out for a test run "around the block" (about 15 miles) and was almost back to 100%. I think I do need to go back and check the spark plugs again for any fouling as it has performance issues under heavy throttle. Can "almost" break the tires loose at dead stop. After restarting a few times no codes were thrown. So I think I've finally squashed this bug. I'll actually replace the Knock Sensor as it is damaged from excessive heat from the previous headers. Which, btw, the new ones, the BBKs, are working great so far.

As a summery, the changes were Timing Chain/Sprocket (because why not, 170k miles), VVT Phaser Gear, VVT Solenoid, Coil Packs, Plugs. There were other issues along the way, but they aren't really important to this particular situation

So now I get to see over the next few days what happens. Hopefully this is the close of this chapter.