The V6 3.9L isn't great for mpg on the hwy. It has high rpm's while going over 50mph. In all honesty, Dodge should have put an OD in the tranny for the 3.9L.

The V8 5.2L with OD get better mpg than the 3.9L without it. Even the EPA fuel charts show this.

Our B1500 2000 V6 3.9L Ram Van got lousy mpg. The B2500 HD suspension (really heavy weight frame) with the 8-lugs, has the V8 5.2L, the 46RE tranny and the 3.92:1 rear. After a few minor and major tweaks to the van, it hit 19.7mpg on the hwy. Only one other Ram Van I know of has ever hit that high. David in TX with his 20+mpg big van.

My thread on how to improve the mpg has a few easy things to do that are trivial in cost. Other mods require an investment. https://dodgeforum.com/forum/dodge-r...rovements.html

Three things you need to increase mpg.

1. Reduce as much friction as possible.
2&3. Air and fuel.

 

Yes the van is like where is the OD dude, I get 16.6 MPG driving at 65 MPH and then that drops if I am in a rush to get somewhere and push 70 MPH

 

My highway mpg takes a steep nose dive when my speedo registers above 68mph which is more like 65mph actual.

 

I would agree with the 60 or above mpg drop off event with our vans no matter it it's with TB or Magnums with fuel rail to each injector. However, I can now do 75mph and not tank the mpg since the Magnum engines have a TB inlet mod to help. BUT, I stay around 60mph since I'm not all that trusty on large vans and roll over issues.

 

My van is properly tuned, friction is low. I even have an electric fan to eliminate loss at the water pump.

How can O/D be added to a B2500 with a 3.9 without exceeding the value of the van? If O/D equipment bolts into a 5.2 shouldn't it also work in a 3.9?

 

I think they might have intentionally not offered the O/D transmission with the 3.9 as it might not have the torque to sustain highway driving at that ratio, but who knows what will happen when you get the bean counters involved.

 

You might consider having your transmission adjusted and the tps set up a notch or two. I just recently had this done. It "seems" like I may have gained some mpg improvement. Too early to tell for sure. BUT the driveabillity has improved tremendously. Very little to none of the hunting gears. Also, by just managing the throttle pedal you can hold it in a gear longer, or feather it and shift on up. Look into some taller tires that give a highway speed of about 65 mph at about 1900 to 2000 rpm. That should help put you better on the torque instead of too far ahead of it.