New guy here. This site is awesome.

When I'm running down the interstate at 75mph, the engine is turning 2400rpm, pretty much on the button. This seems kind of fast to me. Particularly since the fuel milage goes down hill at these speeds. I was wondering if anyone else w/ my same setup can give me some input on their engine speed at this highway speed, or even other highway speeds?

The rig is a Dodge 2006 - 2500 Quad Cab - Shortbox, 4x4, 6spd. It is suppose to to have the 3.73 gears. (The high engine speed is making me second guess this). I have stock tires and wheels, LT265's I believe.

Any input is appreciated...

 

Welcome Aboard.

Your engine speeds are not out of line for your gears and tranny. Those rpm's won't hurt the engine any, but as you've noticed, it will take a toll on fuel consumption.

I've got 4.10's on my NV5600 equipped truck and see about the same rpms at that speed. The older 6 speeds have a higher OD ratio.

My truck gives me the best fuel consumption right around 2000 rpm (low 60's mph). It might be even better at lower rev's but with 4.10s I wouldn't be going very fast on the highway.

 

You have the G56 transmission. IT is a pulling beast, but not the best interstate cruiser (empty). Your rpms sound normal for that tranny.

 

FWIW, I'm seeing 2100rpm @ 75mph....on my auto.

 

I'm new to all the acronyms..... So I just googled G56 and found some interesting info. As I understand it the NV5600 is the older 6 speed? My brother has an 2003 6 spd. His highway rpm's were lower than mine, which is what made me ask the question. I found some talk about the G56 finial drive being about 8% lower than the NV5600. The 8% is about what I see different on my brothers rig.

Thanks guys!

From another thread on this site.
https://www.dieseltruckresource.com/...p/t-93225.html

The ratios of the new G56 are a tad lower than the 5600 as well - the 5600 number is first, then the G56:
1st - 5.63 - 6.29
2nd - 3.38 - 3.48
3rd - 2.04 - 2.10
4th - 1.39 - 1.38
5th - 1.00 - 1.00
6th - 0.73 - 0.79
Rev - 5.63 - 6.29

1st is a lot lower, but the higher gears are quite close. 4th and 5th are the same or nearly so, while 6th is just 8% lower. I, too, would rather have a higher ratio particularly in 6th, but you're not going to get much improvement with the NV5600. There's just not that much difference.

 

I put on some taller tires and they made my truck much more driveable. There are startin to be alot more tires to choose from so I would suggest looking into this. Before I changed I could darn near start in 3rd gear now I can start in 2nd and go more than 5 feet befor shifting.

 

Thats what ive been seein with my G56 and ive noticed that between 1600 and 1900 i get the best fuel mileage! At 1900 im rollin around 62mph and the motor seems to love that spot! Im seenin around 18 to 18.5.