I'll be doing my first tow with this truck. Towing a bass boat from NH to VA. My best guess is the boat/motor/and trailer goes about 3500 pounds...maybe a skosh more. Trip will be all sustained highway miles outside of the first 40 miles. Question is...what mode should I be running the trans in. Outside of normal everyday mode...I guess there are 3 other options with the tow/haul button on shifter. No grades to speak of. Thanks in advance!!!!!!

If it was me, as light as your trailer load will be, I would push the tow/haul button until you get to highway speed, then turn it off. Turn it back on for in town type driving. As light as your trailer is @ 3500#, you won't even know its there!

You can run either way once on the highway. Torque converter will lock-up once at highway speeds.

If cruising around town through stop-n-go traffic and the outside air temps are high, you may want to use Tow/Haul to force the torque converter to lock-up in 2nd thru 4th gears. This will help keep tranny temps lower.

The above are my experiences from towing a Seadoo PWC trailer (approx 2500 pounds) all over the Southwest. When towing the 5th wheel trailer (about 11K pound load), I always use tow/haul.

Unless you're grossing about 75% or greater of GCVWR, (16,500 lbs), you will be fine just leaving it in regular mode. That's straight from the GM manual. The Allison does a very nice job protecting itself with no programmer mods.

I pull a 6000 lb TT and the only time I put it in TH is tow get some braking action from the converter being locked up. It works well for that.

You will certainly not hurt the Allison either way with a 3500 lb load.

thats not even a load for the truck just drive it

Since you will be on the highway with no grades the normal mode should be fine. I noticed, though when I towed a trailer just slightly lighter than yours that in the mountains the trans ran cooler in T/H than in normal mode because there were times when for a given speed the trans would select a higher gear but not lock the TC, which tends to build heat. In T/H it would run a lower gear, but lock the TC, keeping things cooler and actually lowering the engine revs at the same time. Just a thought for when you start climbing.

TC

TC

I tow an enclosed sled hauler heavier than that with 35" tires and rarely use tow/haul. The alli does not hunt or shift, it just lugs the hills. Comparitively speaking my trailer is parachute compared to a boat. Put it in OD and drive, you won't even know it's there.

Is the recommendation not to use t/h based on fuel savings? I gotta say that even with my relatively light 6000lb 5th I LOVE the engine braking that t/h provides in traffic and on down grades. This has gotta be saving service brakes and I know by glancing the guages it's keeping the drivetrain cooler (temps outside in the90s here already). I'd not tow without it. I feel safer, more in control and better about the truck lasting longer. Is the fuel savings large without t/h even if I don't lock out od? In stop and go it really gives a semi tractor feel with the touch the brake downshifts..almost a jake effect. Never had an exahst brake so I'm unsure if it operates similarly.

The grade braking feature works in regular and T/H mode. The t/H mode just changes the shift points on the Allison and locks up the converter from 2nd gear up.

It doesn't really matter and it doesn't hurt if you use T/H with a light load. I use mine in T/H when slowing down to minimize brake use.