Oh that's right. I've heard of guys doing that. I have a manual though, so I find it hard to believe your 5 speed automatic Durango should get better gas mileage than my 5 speed manual Dakota that weighs probably 500+ lbs less.

 

People often assume weight has a direct effect on momentum when in fact this is not the case.

There are lots of variables that can cause one said vehicle to perform better than another.

I'd be intrigued to see the gearing ratios between the automatic and the manual.

 

You're right, and actually I could see the weight HELPING under a constant 65-70 mph trip, so long as the road is completely flat (or downhill). I never drive on roads that are flat. I live in far upstate NY and previously in Vermont where there are a lot of mountains.

As far as gear ratio, I'm at exactly 2000 rpm @ 70 mph, 5th gear obviously.

 

Interesting, I'm at 1,800 @ 70
1ca7dfda.jpg

and 1,450 @ 60
b0eaa70a.jpg

 

I guess that could be the difference. Although I'd actually rather have the 3:92 gear ratio so I could be around 2200 rpm at 70 due to the elevation changes on instates 87 and 89 that I drive frequently. There are a few hills I need to drop down to 4th gear on.

And I'm in no way complaining about the gas mileage. Just find it interesting the Durango does better than my Dakota.

 

If I could find my post from a while ago I actually did work and gave the rpms for all the gears and ratio for our transmissions manual/auto and 3.55/3.92/and a 4.10 estimate. Give me bit and I'll try to repost it here

 

I have the 5 speed auto with 3.55s and at 120 km/h it's 1900 rpm.

 

Okay unfortunately I can't find it easily, with as many posts as I have I don't have the patience.

Anyways, I have done it once I'll do it again:

Automatic transmissions with dodge are often the same or similar construction 45RFE is actually a 545RFE, the gearing numbers are the same. The 4(2,4,6)RE are differentish, I'll put those in after the 545RFE so scroll farther down for those. For those bastards (I hate you out of jealousy) who have a manual 5 speed tranny NV4500, I've made you scroll past the automatics.

(5)45RFE

1st- 3.00
2nd- 1.67 (With the 545RFE the kick down planetary gearing is 1.50)
3rd- 1.00
4th- 0.75
5th- 0.68 (545RFE's 5th gear, when your TCM allows it)
Reverse- 3.00

4(2,4)RE transmissions are the same but able to handle different amounts of power

1st- 2.74
2nd- 1.54
3rd- 1.00
4th- 0.69
Reverse- 2.21

Those of us gifted with the 5.9 V8 get the special 46RE

1st- 2.45
2nd- 1.45
3rd- 1.00
4th- 0.69
Reverse- 2.35

Now for the bastards with a stick or the NV4500

1st- 5.61
2nd- 3.04
3rd- 1.67
4th- 1.00
5th- 0.73
Reverse- 5.04

RPM numbers
Now I only have rpm numbers for the 545RFE transmission and axle ratios, your number should be very close or around these numbers if you're tires aren't stock.

3.55:1 @ 70
4th- 2,050
5th- 1,800

3.55:1 @ 60
4th- 1,850
5th- 1,500

3.92:1 @ 70
4th- 2,200
5th- 2,000

3.92:1 @ 60
4th- 2,000
5th- 1,750

For those who are curious 3.55:1 ratios with a automatic 5th gear, 2000 rpms @ 77 mph. Oh the engine loves that, it'll go up hills and not change.

For some of us not great with numbers, I've type a paragraph or two. Traditionally dodge truck/suvs 4 and 5 speed automatic transmissions, have 3 normal gears and 4 & 5th are overdrive gears. The automatics have the lower normal and overdrive gears which causes them to be more fuel efficient at cruising/highway speeds. The automatic transmissions do just that and are good for cruising around and long distance driving. But for the more truck stuff like towing and off-road they are in my opinion completely inadequate.
This is where the NV4500 manual transmission comes in. This 5 speed stick is perfect and at home in a truck, there can always be better things but this is great. Although the gearing is similar to the 545RFE, the NV4500 was created almost a decade before it. It is designed with GVWR of 14,500 lbs. so in Dakotas and Durangos it can is rated to handle 3,000 lbs more then what our GVWR rates us. The lower 1st gear gives significant advantages when towing, and with 5th gear isn't so low that you can still use overdrive while towing in some situations. Plus not to mention every advantage from engine braking, holding gears and intuitive shifting.

I'll edit this post with more information as I remember it or people ask for more. I hope it helps everyone.

 

Not sure if you meant an automatic w/ 5th gear is 2000 rpm at 77 mph, but my nv3500 is at 2000 rpm @ 70 mph. Stock tire size.

 

I fixed it, thank you, I spent all my patience typing that, I couldn't proofread it effectively.