What gearing you need to have depends on how fast you drive. If you drive around my part of the woods, 4.10s are the best, but if you drive on the interstate, taller gears are better. I'm also hard headed so no body can tell me that 3.55s are better for pulling than my 4.10s especially since I use to have 3.55s.

 

anyone made the swap to 3.42's?

 

Yes, I've made the swap. The .79 6th with the G56 was too low for me pulling horses, cattle, rv, etc. I was running 2150 RPM at 70 and it dropped it to 1950 RPM at 70. I picked up a couple MPG's across the board also. I do think the swap is probably the best for 2005, 2006, and early 2007 G56's only. If you had a NV5600, auto, or a new 3.73 G56, I wouldn't do it. You would start lugging the engine pulling hills at 70 mph.

 

My mom who sells DCJ products says the 3.42 is NOT available with manual DRW. For 3500 SRW it is.

 

Its odd you say that. My dad's 3.73 and .79 is a much better setup for towing thru the hills than my 3.73 and .73. He can do anything at 2200 rpms and often 1900 isn't quite enough and it forces a downshift.

 

I don't mind downshifting to 5th when needed. However, I do mind not being able to run 75 on open highways unless having engine rev at 2400 rpm's though. For people who tow in 60 - 65 mph areas, the .79 final drive is probably the best.

 

I'm glad it works for you, to me the 202 rpm drop at 75 wouldn't be worth the need to run 5th at 60.. but I guess it depends on where you live. My dad seems to still get better mileage than me at fwy speeds, basically same trucks but mine still has less than 20K, and thats with his .79. Personally I want to put a gear splitter in to get that .78 or .80 OD ratio for mountain towing. The double over would just be a empty benefit, but the .78 or .80 OD would be the ticket with 3.73's for mountain towing. The lack of acceleration while towing heavy is another reason I don't think I would swap, a gear splitter only affects your gears when you want, but a gear swap will affect all gears, resulting in slower acceleration when towing, which is why the 3.42 trucks have a 1K lower tow rating from the factory than the 3.73 trucks.

Whats really amazing is that you can get a 3.42 truck with the .74 G56, thats only 2080 at 75... based on my experience that means that you will have to be doing better than 70 to be able to pull hills in 6th while towing, or drop to 5th which is 2450 at 65mph... doesn't seem like a good towing setup.

 

my truck will pull up to 26k at 65 mph in 6th no prob...i would still like the 3.42 setup because i can always downshift to direct and have a more wide variety of pulling speed. plus it would be nice to cruise at 7-75 mph and get decent mileage unloaded

 

In the flats and small hills I have more than enough power in 6th at 65, its just that there are lots of big hills around here.

IMHO a splitter is a better option than regearing, thou more money... and on a .79 G56 you don't get the extra gear of 5th Over. 6th over would be a .616, or the same as a .79 w/ 2.90, so maybe a little low.... The thing I don't like about 3.42's is how they affect gears 1-5. Each gear is 8% taller, which will have an effect on towing. I am very happy with the 1-5 and 3.73's, and really 6th is great, but there are a few times I wish it had a few more rpms...

What would be great is a 7 speed... 1-5 could stay the same as the NV5600, then I would like to see a .80 and .65 for 6 and 7.... Good mountain OD and good flat OD. Thou the splitter would give me .78, .73, and .57.. or .8, .73, .58

 

I agree I really wish my g-56 had a 7th gear around .68 would be perfect, then I could throw on some 285s and get rid of the 35s (only running to drop rpm, even though they look good)

 

Driving style for many is based on speed when in reality it should be influenced mainly by rpm. 1750-1900 is the most efficient range (03-07) (07-08 6.7 is a little lower) with the best mileage being yeilded at 1800 rpm +/- 50 figure everything based on that and grade pulling based on 2000-2100 in direct and you'll never have a problem. let your gears determine your speed, choose your gears based on the speed you are going to spend most of your highway time at.

remember to leave yourself room to downshift using OD all the time is in-efficient in itself. 2 mpg in proper gear selection the first time at the least pays for itself in fuel savings. ( i can od the math for you @ $3.00+ a gallon)


This is dead-on correct. And why my in-town mileage is 19 and highway 22.
First time I towed I couldn't believe how easy this truck was to drive in the rolling hills I spent the afternoon in . . . and got to love that rack-and-pinion steering as well!

I wouldn't change gears (though someone else might) as with my light trailer I could (if I chose) really blast along. But the gear splits were simply ideal, it was easy to "tell" that a heavier trailer wouldn't be that much work compared to the Freightliners I used to drive.

These trucks make it childs play.

This same trailer, behind a big block Chrysler back in the early '70's would be yanking open the secondaries for some real long minutes. Watched the gas gauge go down in real time. ThermoQuad! and an overall best of 8 mpg in a sub-5000-lb car with 3.23 gears.

Would I have changed those gears? Yes, to about 3.31 if I had an overdrive to tack on the back of that 727 AT. Or not. 3.20 to 3.30 was about ideal with that motor & cam and torque converter.

Some interesting stories above. Some of you even know what you're talking about.

 

I am trying to decide between a Gear Vendors unit or a 3.42 swap. What are the gear ratios each would give me? Which would provide the higher final ratio? What is the price difference on these?

 

I plan to add the US Gear OD unit in the future, its a .8 vs the GV .78.

At 75mph you should be at 2200 right now. With the GV it would be 1725 and 3.42's would be 2025.

What sucks about the GV and G56 is they are both about the same OD, .78 vs .79, so you don't get a 5th over better gear for towing and hills.. Where the NV5600 and a GV/US gives you a 1:1; .78/.8:1, .73:1, and .57:1

I still think the GV/US is the best because it gives you the most options on a G56 you have 9 useable gears and a NV5600/ Late G56 has 10.

 

What do you mean late G56? I have a 2007 5.9 with a G56 so I'm pretty late I think. Are the late G56's geared lower (higher?)?

 

Yes there are 2 models of G56. Very few late 5.9's have the new G56 with a .74OD, all 6.7's have the .74OD G56.