My 2010 4x4 Surburban LT shifts down out of overdrive on relatively gentle uphills. I try to cruise around 75-80 and it seems the engine does not have the power to stay in O/D. I would understand if I was driving in Colorado, but I live in Oklahoma and the hills are not steep. No other car or SUV I have driven here has done this. Any ideas on what could be going on. Thanks.

 

you have the 6 speed so it will shift a lot more vs a 4 speed like you are probably used to. 5th and 6th gear in the 6 speed is really for crusing and cannot sustain 75mph up any type of hill. Another reason why the whole 6/7/8 speed transmission craze is like snake oil if you ask me... a guy I work with has a 2010 Chevy truck and it seems it is shifting a lot also.

 

Welcome to the forum.

Concur w/ ousig2408. My 2010 Tahoe will drop to 5th at 75 going up a moderate grade. I guess you could go to M and leave it in 6th but will lug the engine. The ECM knows best.

 

Thanks to both of you for the information. One idea as I was reading the manual - On stretches where there are many hills, would it be OK to put it in M and only let it go up to 5? I know I would loose some MPG but it seems like it would save the transmission some stress.

 

I wouldn't recommend it. You'll hurt the engine way more than the tranny.

 

lol M-mode (like a BMW).

on the 6 speed, putting it in M6 means the tranny can use gears 1-6.

M5 means it can use 1-5.

So, putting it in 6th, won't 'hold' 6th... I wish it worked that way, I could paddle shift my tahoe!

Yea, my 6 speed drops to 5th and sometimes 4th up this one hill on 83 near my house, but its normal... the increased MPG and smoothness is where the 6 speed is worth it.

 

I did not know that. I guess that means you can't start off in 2nd gear on slick surfaces. So it only controls upshifts?

 

http://www.chevrolet.com/owners/chevy-manuals/


M (Manual Mode): This position is available on
vehicles with the Hydra-Matic® 6-Speed transmission.
It lets drivers select the range of gears appropriate
for current driving conditions. If the vehicle has
this feature, see Range Select Mode (Hydra-Matic®
6-Speed transmission) later in this section.

Range Selection Mode (Hydra-Matic®
6-Speed Transmission)
The vehicle may have a Range Selection Mode.
The Range Selection Mode helps control the vehicle’s
transmission and vehicle speed while driving down hill
or towing a trailer by letting you select a desired range of
gears.

To use this feature, do the following:
1. Move the shift lever to M (Manual Mode).
2. Press the plus/minus buttons, located on the
steering column shift lever, to select the desired
range of gears for the current driving conditions.
When M (Manual Mode) is selected a number displays
next to the M, indicating the current gear.
This number is the highest gear that can be used.
However, the vehicle can automatically shift to lower
gears as it adjusts to driving conditions. This means
that all gears below that number are available. When
5 (Fifth) is selected, 1 (First) through 5 (Fifth) gears
are automatically shifted by the vehicle, but 6 (Sixth)
cannot be used until the plus/minus button located
on the steering column lever is used to change to
the gear.
Grade Braking is not available when Range Selection
Mode is active. See Tow/Haul Mode on page 2-38.
While using Range Selection Mode, cruise control and
the Tow/Haul mode can be used.

 

Low Traction Mode
If the vehicle has the Hydra-Matic® 6-Speed Automatic
Transmission, it has a Low Traction Mode that assists
in vehicle acceleration when road conditions are
slippery, such as with ice or snow. While the vehicle is
at a stop, select the second gear range using Range
Selection Mode. This will limit torque to the wheels after
it detects wheel slip, preventing the tires from spinning.

 

580 page manual. this thing has more options than the space shuttle.