What did you do to your 2015-2020 K2XX Tahoe/Yukon Today?

[Doubeleive]

Pulled the camper home from a fantastic weekend out in Crozet, VA. My wife and I and our daughter’s volleyball coach (also a fellow camper) had 6 teenage girls in tow on this trip, so there were plenty of laughs and a little drama.

Managed around 8.5 mpg in the Suburban 3500, pulling 7,500 lbs. I’ll take it.


View attachment 457501

what's the axle ratio on that thing?

 

[Marky Dissod]

what's the axle ratio on that 3500?

Bet it's either 3.73 or 4.10 ...

 

[Geotrash]

what's the axle ratio on that thing?

4.10. It’s most comfortable in 5th, and can hold it up most mild-moderate grades, so I hold it there to keep it from hunting when we’re driving over the piedmont areas of the blue ridge. Lots of up/down on I-64 west of Richmond.

 

[Marky Dissod]

Pulled the camper home from a fantastic weekend out in Crozet, VA ...
Managed around 8.5 mpg in the Suburban 3500, pulling 7,500 lbs. I’ll take it.

6L90, then.

 

[Geotrash]

6L90?

Yessir.

 

[Marky Dissod]

4.10. It’s most comfortable in 5th, and can hold it up most mild-moderate grades,
so I hold it there to keep it from hunting when we’re driving over the piedmont areas of the blue ridge.
Lots of up/down on I-64 west of Richmond.

Although I'm willing to bet that you'll disagree,
I take this quote as evidence that your Tow / Haul mode should be recalibrated
"to keep it from hunting when we’re driving over the piedmont areas of the blue ridge."
By YOU holding it there manually, you're engaging the overrun clutches.
Using overrun clutches lowers MpGs AND adds some heat
(not that it can't handle that heat easily!).
If the 'nature' of the program held it in 5th FOR YOU,
the overrun clutches involvement would be avoided.

However, I'm aware that there are certain situations where you'd still prefer to use Manual-5.

 

[Geotrash]

Although I'm willing to bet that you'll disagree,
I take this quote as evidence that your Tow / Haul mode should be recalibrated
"to keep it from hunting when we’re driving over the piedmont areas of the blue ridge."
By YOU holding it there manually, you're engaging the overrun clutches.
Using overrun clutches lowers MpGs AND adds some heat
(not that it can't handle that heat easily!).
If the 'nature' of the program held it in 5th FOR YOU,
the overrun clutches involvement would be avoided.

However, I'm aware that there are certain situations where you'd still prefer to use Manual-5.

Ah! That's helpful to know. Do you know of any place I can learn more about these overrun clutches in the 6L90? I'm learning new things every day!

 

[Marky Dissod]

Ah! That's helpful to know.

Although there will always be unusually anomalous use cases -

I once tuned an LT1-&-4L60E transplant into an early 70s FireBird convertible,
and made the teachable mistake of telling my customer to use 'Performance Mode'
for driving up&down the San Fran hills where Steve McQueen drove his own stunts for Bullitt
(he wound up using both modes depending on how he was driving in those hills) -

Generally, THE MOST VALUABLE thing to tune is ALWAYS the transmission's shift tables.
The point of tuning the shift tables is to make manual shifting as rare as reasonably possible.
'Reasonably possible' should NORMALLY mean 'NEVER', except for very unusual circumstances,
which I'd concede would likely apply for 2500 & 3500 vehicles.

Do you know of any place I can learn more about these overrun clutches in the 6L90?
I'm learning new things every day!

Although by now it damn well ought to be available in .pdf, I'd guess that
there should be some Field Service Manual equivalent for the 6L80 / 6L90 specifically.

 

[Doubeleive]

I just think that with 4.10 gears you should be good to go unless you are going up a steep upgrade a best of 10.2 seems pretty low
if it is the "thinking" of (saving the transmission) then pull it and have it built for towing by a reputable shop.
there are critical upgrades to the 6l80 that should be done, cheaper to do it while young
but...that's just my thinking and I don't know diddly about many things.

 

[Geotrash]

Although there will always be unusually anomalous use cases -

I once tuned an LT1-&-4L60E transplant into an early 70s FireBird convertible,
and made the teachable mistake of telling my customer to use 'Performance Mode'
for driving up&down the San Fran hills where Steve McQueen drove his own stunts for Bullitt
(he wound up using both modes depending on how he was driving in those hills) -

Generally, THE MOST VALUABLE thing to tune is ALWAYS the transmission's shift tables.
The point of tuning the shift tables is to make manual shifting as rare as reasonably possible.
'Reasonably possible' should NORMALLY mean 'NEVER', except for very unusual circumstances,
which I'd concede would likely apply for 2500 & 3500 vehicles.

Although by now it damn well ought to be available in .pdf, I'd guess that
there should be some Field Service Manual equivalent for the 6L80 / 6L90 specifically.

Blackbear has tuned this one for me already, and I asked them to tune it for towing. It doesn't hunt, really. It's just that when the topography looks more like a sine way in profile than a pancake, it translates to downshifting every other mile as it has to keep speed on the climbs. If I run in 5th, it rarely ever needs to shift. I've read over the years that this is perfectly acceptable practice, until now.