I have a 2004 Chevy HD with the Duramax engine (LLY version if it matters)
and the Allison Transmission with which I pull a 5th wheel camper. We go
camping in Tennessee every year (Fall Creek Falls State Park - Beautiful
Place) and of course we have to travel up and down some steep mountains.
The truck tows the camper without any problem except when traveling down a
steep grade. Almost as soon as I start braking to keep from building up too
much speed, the transmission automatically downshifts causing the RPMs to
jump sky high, a few times even into the red. I know that the transmission
is supposed to downshift while in Tow/Haul mode but it seems like it should
allow me to slow down enough with the brakes before downshifting to keep
from red lining the RPMs. I guess my question is: Am I doing anything wrong
and will it hurt my truck if the RPMs jump up to the red area every now and
then? In doing a little research, I have found some programmers/chips that
claim to help with the downshifting problem. One even says "Virtually
eliminates downshifting while towing". I'm not sure I want that, but if
anybody has any recommendations on a good programmer/chip, I'd love to hear
about it.

Thanks,
Cory

At 2004, it's going to be under warranty - I'd be contacting the dealership
pretty quick and getting the 'issue' documented with them as a potential
warranty claim. At least if SOMETHING happens a year or so down the road
they can't say "but you never told us!". Know what I mean?


"Cory" <news4cnd (AT) cox (DOT) net> wrote

Greetings,

Just as a precaution I would take it to your dealer and ask them is anything
is wrong, but from your description I would say that it sounds like it's
running as it should. This sounds completely like a operator-induced issue.
When in Tow/Haul mode as you describe, the tranny is doing exactly what it
is supposed to do and is giving its best effort at helping to save your
brakes. A brief excursion into high engine RPM's will not hurt your truck
because it's not staying at that level. If you want to avoid going to that
level in the first place then start slowing down before you build up too
much speed, that way your engine will not rev as high when you apply the
brakes.

Regardless of how capable your truck is, 5th wheels are heavy and carry a
lot of momentum. Better to shave off the speed early than to try to slow
down after you've already sped up too much. Anyone behind you who doesn't
like it can just get over it.

Cheers - Jonathan

"Cory" <news4cnd (AT) cox (DOT) net> wrote

You have two red rpm zones, the "dashed" section, and the solid. you can
safely use the dashed section with no harm to the engine, you will not have
any power in this range, this is by design. Do not run the engine in the
solid range under any curcomstances because you will harm your truck.......

sounds normal to me.....


"Cory" <news4cnd (AT) cox (DOT) net> wrote

I'm in agreement with the others, sounds pretty much normal. I have the 8.1L
w/ the Allison and tow a 32' 5'er. I will not tow, even on flats, beyond 70
MPH. It's not worth my family's lives or risking other's to get there only a
few minutes faster. Going down the mountains . . . as the other poster
stated it, they can just get over it. They don't have 16K pounds to keep
under control! Mine has never hit into the red when braking itself. Another
key point is I don't generally have it in tow/haul mode unless in stop and
go traffic. This prevents it from downshifting as quick.


"Cory" <news4cnd (AT) cox (DOT) net> wrote