Overdrive

[Stan]

Mac-2....That's interesting. Mine works as I posted above. Maybe GM /Allison changed the specs in the newer model transmissions.

[Lloyd]

That's odd your truck doesn't go into 6th even at 65mph.
Seems like mine shifts into 6th somewhat after 55--58 mph. (In T/H mode)
I will have to check that out a little closer next time I'm hooked up.

[Stan]

I guess I need to eat some humble pie! I stand corrected on my truck going into 6th in T/H mode. I tested it today and Mac-2 was correct. I don't use T/H on the freeway and assumed incorrectly. When in T/H, the trans did not go into 6th (up to 65 or so). If not in T/H, the trans will go into 6th, and if you then select T/H it will stay in 6th until the trans needs to downshift and then it will stay in 5th. I did not test a faster speed to see just when the trans DOES go into 6th when in T/H.

Thanks Mac for straightening me out!

[Lloyd]

They must have did some changes since mine was built. I just went out and tested it. In the trailer mode, it shifts into 6th at 57 or 58 mph. Has approx. 1700 rpm.

[r2millers]

Originally Posted by artgpo

My Duramax/Allison combo recommends Tow/Haul when towing. I nevertow without being in T/H mode. In my model year it works inconjunctionwith the cruise control to help maintain downhill speed. Newer models like Keith's 2012 have an engine brake.

Lot's of talk about tow/haul mode here but Kenny B's truck isn't set up with tow/haul, just an overdrive setting. This is different from the current t/h options as discussed.

I know the owners manual recommends using 3rd for heavy towing, not keeping it in o/d mode that year.

[Indy_Smiths]

Originally Posted by Old Farmer

They must have did some changes since mine was built. I just went out and tested it. In the trailer mode, it shifts into 6th at 57 or 58 mph. Has approx. 1700 rpm.

Do you have the Bully Dog programmer? Doesn't it allow you to make changes to shift points or choose other shift programs?

[artgpo]

Driving w/o T/H @ 62 mph = 1,800 rpm. Towing RV w/TH @ 62 mph = 1,800 rpm. Would this not indicate both in 6th gear?

[Lloyd]

Originally Posted by Indy_Smiths

Do you have the Bully Dog programmer? Doesn't it allow you to make changes to shift points or choose other shift programs?

Yes, I have the Bullydog. I installed it probably 5 yrs ago, and have to admit nothing has been changed on it since the initial install. I haven't even went in for updates. There hasn't been any problems, so I have just left it alone. I don't remember changing any shift points when it was installed.

Art, I would sure think you have the right assessment.


Edited by: Old Farmer