Will be towing my 7K lb 5th wheel next week up some forest service roads and climb about 3,000 feet and travel 10-20 mph over about 15 miles.

Should I use tow/haul or manual in 1st gear? and why? And what transmission temp is too high and time to pull over.

Will be towing my 7K lb 5th wheel next week up some forest service roads and climb about 3,000 feet and travel 10-20 mph over about 15 miles.

Should I use tow/haul or manual in 1st gear? and why? And what transmission temp is too high and time to pull over.

That's a great question that i'd like answered as well. My brother has a 7.3L PSD that he has chipped and allows him to lock the TCC in first gear. He tows his ~10K TT up forest service roads alot. I went with him last year, and he has NO heat issues with either engine or tranny. He does use 4wd HI range, for traction purposes on the steep dirt roads.

I was wondering how my LMM would do under a similar test. I figured I would want to use 4 LO to allow the tranny to be in a gear above 1st. The TCC doesn't lock in our trucks under any circumstances. with Tow Haul on it will lock in 2nd thru 6th.
Big question is does 4 LO change any of the Tow haul parameters for TCC lock??

Anyone who has towed like this???

Just put it in Tow/ Haul mode and drive it an auto. A 7K load is nothing for an LMM. Not sure what the temp would be before you need to shut it down, but doubt you'll get there anyway...even at those low speeds and high altitude...just my 2 cents..

From mountain experience (not on forestery roads)
7k is not that much to sweat over.

Use T/H mode in manual and bring it down to hold 2nd or 3rd.
Keep rpm's 2000+ when pulling up the grades and let the engine break on decents. From other threads, engine breaking rpm can safely climb to 3500-4000 (up to 4600 max) if necessary.

I doubt temps will be a problem

IIRC, max torque is at 1600 rpm, but tow/haul is your best bet. 4H if your rear wheels start slipping. I like manual going down steep hills, redline downhill is something near 4000, but it won't let you redline it. Remember, T/H downhill has a speed-control feature (at least on LMM).

Personally, I'd put it in TH and D and let it make the call. They had to of thought of this scenario and had a reson to not lock the converter in 1st. I'm guessing it could be done, but I can't imagine towing in 4L. I think you will be more than ok with 7500. I have pulled mine up a pretty steep hill to my place a couple of times and had no problem up to 30mph. Probably could've gone faster, but not with the turns.

I think the tranny will limp itself somewhere around or above 260.

I tow doubles(10k 5er with 3-4 atv's) up forest service roads at the same speed(about 15-20 mph)in 4h and in 2nd or 3rd gear(manual). It's 12 miles to the top and I just take her easy and have never had a heat problem.

Thanks for the replies. I'll go with t/h and take it easy. The last hill is a transmission killler. People go up in D and overheat.

Thanks for the replies. I'll go with t/h and take it easy. The last hill is a transmission killler. People go up in D and overheat.

Those people don't drive a DuraMax. Just be in Tow Haul!

Man,I pull 15,000 lbs ,just let the Allison do it for you in tow mode.No need to manual your self to death with this rig.

Report back and let us know how it goes. Low speed stuff is killer with no air moving through stack. If it does start to heat up try upping the rpm's if you aren't already in first. Or take a break. Usually at slow speed though it heats up quick if it is going to.

Fan will start roaring but that's by design. It's a good sound.

Well here is the report. On the first hill hit 204 and 228 on the second. Fan came on the second hill. I was in T/H then shifted to M2 once I hit about 220. Then shifted to 1st @ 225. Should I be worried about 228? Ambient temp was only about 65.

You can be in T/H AND M2 at the same time. Maybe you were and just not clear

The T/H will allow less trans slippage regardless of gear selected in M or D is my understanding. It will also assist in slowing on decent.

Put in T/H and drive it and don't worry it will be fine.

Yup I pull a 14000 lb 5er allover the Rockies and just use the tow/haul mode....No problems.....a 7000 lb trailer is a piece of cake.....

They are warm I think, but to be expected with the grades you speak of and little airflow from speed. Someone with more knowledge than me will chime in, but I wouldn't start to worry until 250+

I agree with the other guys, whether D or M, make sure you are leaving it in TH.

Well here is the report. On the first hill hit 204 and 228 on the second. Fan came on the second hill. I was in T/H then shifted to M2 once I hit about 220. Then shifted to 1st @ 225. Should I be worried about 228? Ambient temp was only about 65.

There is some cause for concern with tranny temps at 228.
From everything I've read or heard conventional tranny fluid starts breaking down with temps that high.
As far as the Allison goes, from everything I've read it can take the heat, as long as it has good lubrication.

I'd suggest converting your tranny fluid over to a synthetic TES 295 fluid. I'd also be a little concerned about the fact that ambient was only 65. If you make the same in mid-summer I'd be a little worried.

I had it in T/H the whole time just shifted from D to M.