the 5.9's wether auto or manual ran the same power, however since the 6.7L has more output the engine was derated to save the G56 tranny from ultimate doom.

 

why would they derate the manuals. I know they used to derate the automatics (03-04.5 to get the HO you had to have a manual. 383's doesn't seem right to me either.

 

Not sure why the manual is derated except as Drew said, "to save it from ultimate doom."

I think he means the 3.73 gear ratio. For 08, the standard ratio for the manual is 3.42 with a 3.73 option. I think the 4.10 is not available for the manual since it is already geared so low.

 

How has your 6.7 been Saber?

 

My truck was built 02/07 and purchased new 06/07. I now have 11,000 miles. At 4700 miles I had a CEL (P2262) which resulted in a new turbo. Since then, I've had no more CELs. I've kept up with the new flash versions as they came out and had the G30 recall done.

MPG is lower than my 2004.5 5.9L. I get 15-17 city/highway (even with 3.73 gears).

Overall, I'm satisfied with the truck. I especially like the smooth shifting 6-speed auto. If I had it to do over, I'd buy the 6.7L again.

 

I will go and drive an auto today. I am just afraid that theweight that I pull will kill it, we gross up to 26k regular on 125 mile hwy trips, I know the trucks are not rated for it, but my 04 seemed to like it. Are you towing anything? Thanks

 

it is all about the input torque of the tranny and it not being rated to handle what the 68RE can.

 

Sabersix,

What do you mean the 04.5's were derated for the auto and you could only get the HO in manual? I have an 04.5, auto and it's the HO (the 600 engine) 325 HP, etc, etc. Nothing anywhere in the manual or sticker etc that says anything about derated.

I was tempted to test out an 07 6.7L, but I want to do a lot of mods to my truck and I prefer to wait till the warranty is over to start doing things to it, so I think I'm gonna keep my 04.5.

 

Sorry for the confusion. It is only the manual transmission with the 6.7L engine (07.5 - 08) that is derated.

 

I'm not towing anything, but I have read (on here and in other forums) that heavy haulers really appreciate the new 6-speed automatic with the exhaust brake. It supposedly works very well in tow/haul mode to control the load with aggressive exhaust braking and appropriate downshifting.

I thought I wanted a manual transmission until I test drove both. The 6-speed auto is smooth and seems to be in the right gear at all times;much different from the 4-speed auto which seems to have a big gap in power between 3rd and 4th gear.