Just purchased used 2004 GMC 3500 D/A with 15K on it. Haven't had a chance to read manual but was wondering if towing a 9700 lb fifth wheel in 5th gear (OD) was OK. My previous truck was a 1996 Chevy dually with the 7.4 gas and I talked with a number of people who insisted you shouldn't pull in overdrive or "bad things" would happen to your tranny. Getting a Duramax is a dream come true. Can't wait for my next trip down to Yuma on I 15 without the endless down shifting I got in the 96'.

Just leave it in drive, put Tow/Haul mode on, and let the truck and transmission do its thing. ;)

Welcome to the Diesel Place, good luck with your truck!

-Ben

5th gear, OD, Tow/Haul, Cruise is the only way to fly. Don't lug it if it needs to downshift on a hill, but if it feels strong, by all means do it.

i pull a cat D3 dozer in tow/haul and it goes into 5th from time to time

If the load isn't big then don't bother with tow haul even.

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Unless you doging it on hills you should be fine in drive.. I pull my 13,400 lb full profile 5er in drive all the time... On flat to rolling roads... On the big stuff I go into Tow/Haul...

Been pulling it this way for about 25,000 miles and no problems so far ....

Well unless you count that damn fan roaring all the time :)

"Lock It and Rock It" in 5th. The days of only towing in direct as a top gear are over in my book!

Thanks for the replies. Did some reading on the Allison tranny last night and am pretty impressed with the "smarts" they built into it.

:ro)

The tranny is idiot proof, like they said 5th / tow haul and go.

The tranny is idiot proof, like they said 5th / tow haul and go.

Yes it is, it just isnt horsepower proof. ):h