I tow my 28' travel trailor alot in summer months, but rarely use the tow mode or disable the overdrive. The duramax tows so nice I usally forget I even have a tow mode. Is this bad for my tranny, should I use it even if I am only towing around 7000lbs? What about the overdrive under what conditions do you disable it??

I tow a bobcat trailer all the time and I always use the tow/haul mode. If you haven't noticed it downshifts and helps you slow down easier. It also locks up the torque converter so it isn't as hard on it. I have never used the overdrive disable feature.

Tow/haul will lock the TC under some circumstances where the regular mode won't, reducing slip and temperatures. For example, I was climbing a long hill going to Kings Canyon with a light trailer with T/H off. I noticed the tranny running a bit warmer than usual. Out of curiosity in hit the button and the trans immediately downshifted then locked the TC and the engine revs were actually reduced and the temps went back down.

TC

If you are in 4th or 5th gear and just cruising the flats, I won't make much difference. The torque converter will lock with or without tow/haul. Grade braking will still engage and function the same until you drop to 3rd gear. If you need to drop to 2nd or 3rd gear, you need to activate tow/haul so the torque converter can lock. The same goes for a long climb that requires 2nd or 3rd for extended periods. If the converter is not locked, the tyranny fluid will heat due to the slippage. The converter always locks in 4th and 5th so the only difference is the shift point. The only reason to use the OD lockout is to stop the transmission "hunting" or shifting from 5th to 4th and back. In some conditions, the transmission can't make up it's mind which gear it wants to be in. The OD lockout will force the transmission to stay in the lower gear and end the hunting cycle.

The Allison is one smart transmission. ;) It feeds off data supplied by the PCM and adjust accordingly. When in tow/haul mode you are telling the PCM/tranny that there is additional load on the vehicle. The tow/haul mode engages grade braking differently than normal mode, the shift points are higher, and the tranny knows when to shift/downshift based upon operating parameters specified in the PCM. In a nutshell the dang thing is probably smarter than we are when it comes to all the above! ):h

I for one take advantage of the technology built into the truck and always use tow/haul when towing anything of significant weight, say 5k lbs. Yes there are times when I need to override the overdrive, especially when towing very heavy at lower speeds, say 45-55. IMHO GM did a freakin outstanding job with the Allison 1000 series tranny's in these trucks. JJ's .02 cents worth. JJ :)

thanks for the info, so is it okay to cruise at 60 or 65 in tow mode or do you take it out when not needed. does the tow mode lock out the overdrive or can you do both?

I agree the tranny is amazing. sometime I wonder who's really in control me or the truck.

T/H mode does not lock out Overdrive, that is a different function. T/H is safe to use at any time or at any speed. Some here even do all of their city driving in it because they like to results.

Kelly

In the example above I was towing a very light trailer 2500-3000lbs. So light that I didn't think there would be any benefit in T/H mode. I was wrong. JJ is right the Allison is much smarter than we are. Now, whenever the coupler is on the ball the T/H is on.

TC