I have an old 12valve, with a 5 speed (well, they call it a 4 with granny). I'm thinking about upgrading the truck (Ok, so I'm getting old... noise, creature comforts, less rust etc.) in the next 6 months or so, but I don't want to take too big a hit on fuel economy.

Is there still a big difference in economy for auto vs. manual? I know auto tech has improved a lot in recent years.

Also, for newer trucks (and yes, I know there are other variables) say 2002 and newer, in general, which gets the better fuel economy?

 

some say the 03-05's get the best milage due to the fact they dont have the 3rd injection. if you get an auto, be sure its a 48re. i think most prefer a manual. stay away from 02's because they have the dreaded vp-44s

 

I have a 04.5 with just a Power puck Auto. See sig. I average about 21 on the highway and and around 19 in the city. Most of my driving is on the highway though and i have 4.10. If you do a search you will find the conversation say 3.73 with a manual is the way to go. I just happened upon my truckand it was such a good deal.

 

Manuals will get you quite a bit better mileage. Thats all I have ever driven is a manual and friends of mine have same truck but with AUTO... They get 1-3 MPG less

 

Slippage through the converter aside, an auto has a lower overall final drive ratio in OD - the reduction in cruising RPM sure helps to raise mileage.

Fuel economy improves with a tight, low-stall locked auto (read built) tranny, and of course tall, narrow ribbed-tread tires are very beneficial for steady-state driving.

The CTD "sweet spot" for low BSFC is ~1900RPM, although down to 1700RPM nets the best mileage due to the lower wind resistance.

I'm getting 20mpg highway with the heavy 37" Toyo MTs.

 

Well, can't talk to the other, but for the 06 G-56, the six speed manual probably gets a little worse mileage on the highway because of the gearing. The 07 has better gearing for the G-56 and will do much better on the highway.

 

Dunno about that. I'm getting between 18 to high 19's on the highway (empty of course). Some of it might be the wind resistance, though. Blasted wind out here.

 

Yep, they changed the gearing in the G-56 in the 07. At 65 MPH, I'm at about 2000 RPM in the 06 (with the stock tires). I am getting an average of 15 MPG in this truck, with the stock set-up the best I got 1 tank was a little over 18. Wish I had the gearing in the 07s...

 

Manual all the way... Dodge never did and still doesn't make a tough enough automatic in my opinion.

 

Yea, I was fortunate to get a 5.9 with the updated G-56 the Last digits on my trans are AE. It's what they put into the 6.7 manual trucks. My truck was made in LATE Dec 2006 so has the 5.9 with the new trans.. LOVE IT!

 

Don't know what Dodge was thinking when they made the gearing in this 06 G-56? Glad to see it only took Dodge 1 year to fix it, really wish they would have got it right when they first released this transmission...

 

That can be argued. The G56 is geared a little too low for good mileage at higher speeds, but my truck gets excellent mileage (19-20mpg)at or below 65. These trucks were designed to work hard, and if you tow 9000+ lbs that gearing is excellent.

To the original poster, it will depend how you use your truck. If you typically run a little slower you will get better or equal mileage out of the manual in a G56 truck. I personally like a manual in a truck.

 

I got 26.5 mpg on paper with my 06 auto last trip one way, on the trip back 24.5, the 26.5 is the best ive ever got, but im running a 2 wheel drive, 65 on cruise. empty, I really am impressed with this truck, shes a keeper.

 

Spoken like a man who's never driven a 68RFE truck. It will change your mind about Dodge automatics.

jmo

 

Agreed, I test drove a 07 with the 68RFE and it was hard for me to walk away, but once I read all the ck engine lights on the 6.7 motors at that time, and few 5.9's left, I jumped on the 5.9