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I just towed with my 2017 Z71 4x4 long bed diesel Colorado for the first time. Temecula, CA to Peoria, AZ and back with a 6x12 Uhaul weight 1,800 lbs, fully loaded and the bed of the truck loaded as well. I figure it was about 4,000 lbs. 350 mile there an 350 back over 36 hours. 75 mph most of the time. No problem getting to 85 to pass whenever I needed to. I was in tow haul mode with the exhaust brake on all the time. Got about 17 mpg on the way loaded, but only 15 on the way back unloaded because we were heading into the teeth of some pretty bad wind all the way back. My main question is should I be in tow haul mode with the exhaust brake on all the time when towing, or is there some reason to be out of tow haul mode sometime when towing when not on hills on mostly level roads at speeds over 70 mph? Does the weight of the load dictate that I should always be in tow haul mode? Thanks in advance for any and all replies.
 

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I pulled the same trailer this past summer from the Twin Cities of MN to Rapid City South Dakota. I got some warning messages about bad quality DEF fluid (never had filled it up since I got the truck) and then my speed would be reduced. I was in tow haul mode as well. Took it to a dealer, they said my truck wasn't regen'ing, so they forced a regen, cleared any codes, test drove and no more warnings. Worked great until heading back home from vacation and got warning messages again. Anger would be an understatement. My speed got reduced all the way down to 55mph, before message went away and I had full power. I took pictures of all my warning messages to show the dealer when I got home. On the way to dealership a couple days later, got warning messages again. They ended up reprogramming ECU, 3rd time in, they replace DEF sensory. I have had my truck in the shop four times for DEF related warnings. In the end, the guy at the shop said, if I'm towing, no need to put in tow/haul mode unless the transmission is constantly shifting and don't put on the exhaust brake unless in a hilly area. Haven't towed since, but I HATE DEF with a passion. Other than that, truck has been just peachy.

Good luck.
 

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When I get up to highway speeds (60+ ), I shut Tow/ Haul off. Unless I'm mistaken, it limits you to 5th gear, so you never get into 6th. If I'm going through hills and curves and needing to slow down or stop, or do a good amount of accelerating, then I turn it back on. But I don't believe it hurts anything turning it off and on while driving. I had to come to a sudden stop one day, it both this truck and our 2008 Chevey Duramax 3500HD (work truck) and with Tow/ Haul on and hitting the brakes, you come to a stop very quickly, loaded or not.
 

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@Burgess159 nailed it. I use it when I’m towing but I turn it off when I get up to speed on flat road. Click it back on when i hit hills or my exit ramp.

Flat interstate towing with my typical load in tow haul I get ~12 mpg, turn tow haul off and I get ~15 mpg. As soon as you turn off tow haul it’ll upshift and lock up the converter.

I use it anytime I’m in the mountains whether I’m towing or not for the engine braking.
 

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Discussion Starter #5
When I get up to highway speeds (60+ ), I shut Tow/ Haul off. Unless I'm mistaken, it limits you to 5th gear, so you never get into 6th. If I'm going through hills and curves and needing to slow down or stop, or do a good amount of accelerating, then I turn it back on. But I don't believe it hurts anything turning it off and on while driving. I had to come to a sudden stop one day, it both this truck and our 2008 Chevey Duramax 3500HD (work truck) and with Tow/ Haul on and hitting the brakes, you come to a stop very quickly, loaded or not.
Thanks Burgess159. Also, we'll be seeing you in the Cotton Bowl, I think you're a 7 point favorite, but look out for Sam Darnold and Ronald Jones. Good Luck. USC Trojan class of '66.
 

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While towing a vehicle the weight of tow vehicle and the vehicle to which you are towing both should be considered. The towing weight varies with the type of vehicle and it is defined in the vehicle manual. Yes the tow haul mode should be on while towing the vehicle with the exhaust brake as it helps to control the vehicle. For more info one can surf on internet as there are more useful reference available and you can also contact the service providers as they are the professionals they can help you more in this.
 
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