I am getting ready for a trip out to Yellowstone this week and I have, in the process been reading up on tow/haul mode. I have a "new" Chevy 2500 diesel pickup. Everyone says to "set it and forget it" but I have a question- if I travel under 80KM/hour (I am in Canada)- about 50 MPH- the shifting seems too high and the RPM's are higher than I would like. Once I get up to speed on the highway- 60 to 65 MPH- it seems fine. Is this normal?
The Duramax makes more power at slightly higher revs. The tow/haul mode delays the shifting to allow you to stay in the power band longer. Additionally the tow/haul mode causes the transmission to shift quicker which reduces wear on the clutches. I'd leave it in tow/haul. If you really don't like the higher rpm try turning off the tow/haul for a minute to allow it to shift to the next gear then reengaging it. If it immediately shifts back down then the computer is sensing something that tells it that it needs to be in that lower gear.
John (USN Ret) and Debbie
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yep, sounds normal to me. I've got an 08 D/A & when in the tow/haul mode i have to be about 54-55 before it'll shift into 5th gear and about 62 before it'll shift into 6th gear. Once in 6th gear i can go down to about 58 before it shifts back to 5th gear so the downshift point for each gear is a little lower (few mph) than the upshift point. As was stated earlier, you could take it out of tow/haul to get it to shift up, then go back into tow/haul or you could go faster to get it to shift, then slow down a little, but not enough to cause it to downshift. Course if you're in hills/mountains, it becomes more of a challange to keep a constant speed and gear. Then i'd just 'set it & forget it.
If you read your owner's manual, it says under what conditions you should use tow/haul mode. Not sure what year of DMax you have, but I think the later ones say it is somewhere around 75% of your towing capacity. Less than that and you do not need it.
I usually only use it on mine to help slow the truck down, but then I have not towed in the mountains yet.
That being said, I would do what goodcruisin says, only use it if you need it, and you would know that you need it if your truck is constantly shifting into and out of a higher gear.
We just got back from a 1830 mile trip along the east coast. Mostly on I95. On this trip because of the cost of diesel fuel we decided to play with our speed and transmission setting and see how it effected our MPG. We normally drive at 65 mph where our mpg is right at 10mpg. This time we decided to keep our speed at 55 mph. We were pleased to find that, as we hoped, our fuel milage went up. We keep good records and found that our average mpg was between 11.5 and 12.
I guess it was worth it as by my calculations we used 25 fewer gallons of fuel by driving 55 versus 65. Our average cost of diesel was $4.60 per gallon so we saved about $115 on fuel. This is about the cost of a big fill up of our 30 gallon tank.
BUT, since this thread is about tow/haul mode I will mantion what we found about using tow/hau. We played with using tow/haul versus not using it. We noticed that our mpg dropped off about 1 mpg when we used the tow/haul feature of our F-250. I guess it was because at 55 mph the engine constantly operated at higher revolutions. So since I-95 is basically a flat road we switced to not using tow haul.
'05' F-250 Power Stroke
'00' 30' Cameo Fifth Wheel
Krause wrote: I am getting ready for a trip out to Yellowstone this week and I have, in the process been reading up on tow/haul mode. I have a "new" Chevy 2500 diesel pickup. Everyone says to "set it and forget it" but I have a question- if I travel under 80KM/hour (I am in Canada)- about 50 MPH- the shifting seems too high and the RPM's are higher than I would like. Once I get up to speed on the highway- 60 to 65 MPH- it seems fine. Is this normal?
Just wondering.
How "new" is "New"?
Do you have a 5-speed Alli or a 6-speed?
The whole idea of Tow/Haul (T/H) is to raise the shift points, sharpen them up while keeping the Torque Converter Clutch (TCC) locked. All in the interests of reducing transmission temps.
My '05 has the 5-speed Alli and needs to hit 55mph (90Kph) to get into 5th with T/H on. It will hold 5th until it drops to about 52.
If you don't get to where 5th engages I would still drive in T/H until you are at cruising speed, then disengage it. I believe the trans will then shift into 5th and the TCC will lock. As long as it is locked you will be fine. TCC unlocked will elevate your trans temp and reduce your mileage so make sure it does lock up.
Re-engaging T/H would be a good idea when descending hills or stopping as the Alli will do a good job of using the engine to slow you down with much less use of the brake pedal.
Good luck
Keith J, Retired from GM Engineering
2005 GMC Sierra 2500HD SLE 2WD/CC/SB/DA.
1999 Sunnybrook 27RKFS Fiver
Bilsteins, Line-X, Westin steps, Prodigy, Retrax, 16K Superglide, 5th-Airborne pin-box, Multi-vex mirrors.
With a 90KM/H (55MPH) speed limit in Ontario, it is difficult to get the Allison to upshift to 6th gear in T/H. A little trick that I found works real well is to get up to speed in T/H and then take it out of T/H until it kicks up into the next gear. It works everytime and once it's in the next gear, I turn T/H back on. T/H will not downshift to 5th until the truck slows down to about 85 klicks.
Helen & George VE3INB and Max (Bichon Frise) 06 Silverado LT 2500HD D/A 2006 Crossroads Cruiser CF30SK
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