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Discussion Starter #1
First impression:
The LML is a dream to tow with. I hooked up a 18ft trailer and put an extended cab Toyota Tacoma x-runner on it this past weekend. Set the trailer brake to 50% gain, turned on the exhaust brake, and tow/haul mode. I never felt the trailer fight the truck in any way. I've towed many trailers on older rigs and always could feel the trailer pushing the vehicle downhill or coming to a stop. At 70 mph the truck pulls great and feels super stable. Going up long steep grades was easy. the truck never hesitated or dropped down a gear to go up hill. Never had that "needs more power" feeling. It truly was fantastic. I even passed a few cars going up hill.. Even just letting off the accel. pedal, the truck takes over to control the weight. I went down a fairly steep grade and the truck actually dropped down a couple gears and rpms flew up to about 3500 rpms. I probably should have squeezed the trailer brake but I lightly set into the brake pedal to bring the rpms down. Still never felt out of control.

GM did a fantastic job of assembling a vehicle that gives the driver a peace of mind when using the vehicle for whatever task you need it for
 

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Awesome report on how well the '15's do at towing.
 

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I went down a fairly steep grade and the truck actually dropped down a couple gears and rpms flew up to about 3500 rpms. I probably should have squeezed the trailer brake but I lightly set into the brake pedal to bring the rpms down.
Don't sweat the RPM increase on the downgrade, that's your exhaust break in action. No need to engage the trailer brakes or truck brakes if on cruise unless the pucker factor gets too high for you.

I tow a 45' fifth wheel ~21,000 lbs all over the passes in Colorado, I usually just set the cruise control, tow/haul mode, ex-brake and simply steer between the lines. Only on very very steep grades do I tap the truck break, most cases up and downhill I will be +/- 5 MPH of the set cruise.
 

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Discussion Starter #4 (Edited)
Good to know. I wasn't puckering I just didn't think it was good having the rpms that high. I'm new to exhaust brakes... Hell I've never owned a 4 wheeled vehicle that's less than 10 years old haha

Does the truck engage the trailer brakes in when it's exhaust braking with cruise engaged?
 

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Does the truck engage the trailer brakes in when it's exhaust braking with cruise engaged?
No. Trailer brakes only engage with foot brake or manual lever for trailer brakes.
 

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The computer won't let you over-rev it, it will upshift if needed.
 

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I agree with your review of towing with a 2015. I have a 2015 GMC 2500HD double cab. The first week I had the truck we towed our 24 foot travel trailer from WI to Glacier National Park. The trailer weighed about 4400 lbs loaded. I use a Blue Ox weight distributing hitch. It was amazing compared to anything I have used for towing. I have never felt so safe and in control when it comes to stopping while pulling a trailer.

My previous truck was an 03 Chevy 2500HD with an 8.1L and Allison. The 2015 Allison seems to work a lot harder to slow the vehicle down than the 03 did (with the exhaust brake off). Add in the exhaust brake and there is almost no effort required to go from 65 MPH to 0.
 

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First impression:
The LML is a dream to tow with.
GM did a fantastic job of assembling a vehicle that gives the driver a peace of mind when using the vehicle for whatever task you need it for
I second this statement. Towing a 35' fifth wheel has never been easier. I started with an '05 gasser 2500HD. The first time I hit the road with my '15 diesel I was amazed. With the gasser it did the job but I was exhausted after a 2 or 3 hour tow. You had to drive the truck and tow the trailer. With the '15 diesel you simply set the cruise and let the truck do the work. The Allison transmission is a work of art.
 
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