I don't have the 3.9L, but just purchased a '93 with a 5.2L. To break it in got the transmission flushed and oil changed before taking it on a road trip across Washington state - Seattle to Spokane. I set the cruise control on 79 on the way over and averaged 16.8mpg and decided to lower the cruise to 73 on the way home and was shocked when I found I averaged 22.8 on the way back! WAY BETTER THAN I WAS EXPECTING!

So with that said, I'm confused how you're not getting mileage that's at least comparable to mine... I figured you'd be at least equal if not ahead.

 

Like hans5.2 stated above...

 

[/quote]Why not lol? I get off on it [/quote]

that is wrong on so many levels....... I have a mesh net replacing my tail get gives it a 2% boost that i have noticed

 

Only joking and of course not literally. But there are so many disrespectful drivers on the road. Half the people don't use their blinkers. They pull out in front of you, cutting you off and then drive 15 miles under the speed limit. Then there are the tailgaters, and the ones that drive vehicles so big, they don't know where they're at on the road, and can't even get their vehicle in between the lines of the parking spaces. Lets not forget the idiots that don't use their lights when required for safe driving. Like before (and after sometimes) sunset, and sunrise. And during downpours, overcast sky's and fog. And last but not least, the ones who are either hugging the center line or over it on your side of the road. For all these people I have no respect, and If my driving disrupts them..... WHOOPS

 

Couldn't agree more with you G.Man!

And to throw this out here on the subject of Increasing MPG. This is something I'll be getting when I have the cash to do it.
A tonneau cover for your box, it kills the wind drag that your box creates giving you a bit stability when its really windy and it adds dryness and depending if you go for a hard top canopy security for your box. Without the wind drag you should see around a 1-2 MPG increase. I'll be getting a soft one though (Truxedo Lo Pro QT) just for the convenience of not losing any box space when I roll it up and integrated bars with the fabric so no hassle with setting them up.

 

I will consider your transmission fluid idea, but i have a small leak, and if the molecules in the synthetic are smaller on it too, that may cause a problem. I have to use some stuff that thickens it, i think it is made by douglas? It comes in a large white bottle that tapers to a point at the top.
I dont think i will ever try to push more than maybe 7.5k miles, even if the oil is top quality. I want to watch this engine hit 300k, so i take good care of it. I have been using synthetic for a while, so any sludge should have been cleared, and i dont have any known leaks other than the tranny.
I should probably do a transmission fluid flush soon, but since i plan to change the transmission, i will wait until then to do this.

 

Yeah, I'd wait to go synthetic in the tranny if you have a leak. But I'd recommend it when you get a new one. I have only used red-line transmission fluid, so I can't vouch for the others, but you will notice an improvement when switching over. The peace of mind that comes with using high quality synthetics is a plus too. You only change your tranny fluid every 30k, so spending the extra money on quality isn't too big of a deal.

 

yeah i live in tampa fl so i get everyone of those lol and the old farts that cant drive.