Not overly impressed.
Laughing Gas
Joined: Dec 2005
Posts: 906
Likes: 107
From: Seattle area
One other thing to check if you have FORSCAN or another real time monitor. Check the Throttle % (key on engine off) and make sure it rolls smoothly to >95%. Anything (like floormat) possibly stuck under pedal?
Tuned
Joined: Feb 2017
Posts: 394
Likes: 75
From: Alaska
I had a similar experience as the OP. While towing approx 13k pounds across country, I found myself preferring manual mode so I could control the truck a bit better. This was with a crew cab long bed SRW diesel with 3.55 gears. I would have much preferred 3.73 or even 4.10 gears. Course driven was Michigan to Alaska, with plenty of mountain passes.
Laughing Gas
Joined: Apr 2012
Posts: 902
Likes: 51
From: Clark, WY
I had a similar experience as the OP. While towing approx 13k pounds across country, I found myself preferring manual mode so I could control the truck a bit better. This was with a crew cab long bed SRW diesel with 3.55 gears. I would have much preferred 3.73 or even 4.10 gears. Course driven was Michigan to Alaska, with plenty of mountain passes.
Prolocutor
Joined: Jan 2009
Posts: 13,618
Likes: 1,247
From: Western MA
While my truck doesn't exhibit the behavior the OP is seeing, I do notice that when running at 25-30k GCW that my trans hunts more at 65-70. The sweet spot for me with 20" wheels and 3.55's is 75-80 which isn't always possible. Yukon is supposedly testing 4.10's for the Dana M275 which would put me down a few MPH. Not sure it's worth the coin.... Going to 295's the next time around might force my hand though...
Posting Guru
Joined: Apr 2006
Posts: 2,216
Likes: 7
3.55's are ok on flat ground but in the mountains you need deep gears.
And yes I have had 3.55 and 4.30 trucks. The 4.30 trucks pull easier.
And yes I have had 3.55 and 4.30 trucks. The 4.30 trucks pull easier.
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Prolocutor
Joined: Jan 2009
Posts: 13,618
Likes: 1,247
From: Western MA
It's not something that the average backyard mechanic can do. However, for a competent shop, it's not a big deal at all. One thing to remember is that on a 4X4 truck, you have to do the fronts too which doubles the cost.
Thread Starter
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Cross-Country
Joined: May 2018
Posts: 53
Likes: 4
That’s pretty much what i figured. It’s not like I pull in the “Rockies” that often, however, when I do, I want to be able to pass the slow truckers and not be based up by dodges pulling similar weight.
Super Moderator
Joined: Aug 2008
Posts: 37,384
Likes: 1,868
From: Frederick, MD
I too think gearing maybe an issue. Lock out 6th gear on the steepest of grades may help.
I have taken that route many a time with my truck. Although it is not the same, mine is a 2013 drw with 3.73's. Loaded with 16K of 5th wheel I can hold 55-60 all the way to the tunnel and beyond. I have gone both directions and had better luck than you.
Gears maybe the answer.
I have taken that route many a time with my truck. Although it is not the same, mine is a 2013 drw with 3.73's. Loaded with 16K of 5th wheel I can hold 55-60 all the way to the tunnel and beyond. I have gone both directions and had better luck than you.
Gears maybe the answer.
Cargo Master
Joined: Aug 2015
Posts: 2,400
Likes: 15
Doing a quick calculation, your 4th gear with 34" tires and a 3.55 is nearly identical to my F450's 5th gear with my 4.30 and 31.5" tires. I pull at around 2570 RPMs at 65 in 5th, so you should be around 2630 at 65 in fourth. You should have no issue pulling 6% grade at 65 in 4th gear, 2630 is a fine speed for the 6.7.