steep grade, towing, won't downshift into 2nd

[techntrek]

I encountered this with the stock tune, thought the Diablo tune would help with this. Pulling a camper over steep grades today, and hit a few hills where my speed dropped to 30 with WOT and it refused to downshift into 2nd automatically. Held 3rd and 30 mph. I could manually set it to 2nd and then had power to increase speed. My only guess is the engine and oil temps were obviously running warm and if I manually set it to 2nd the temps would skyrocket. Maybe the computer isn't downshifting to manage these temps? Or are there other parameters that limit it in these situations?

Doubly frustrating is with just a slightly less steep grade I had plenty of power to spare and speed wasn't an issue. Its like with a 5% grade I have my full hp/torque, but hit 7% and suddenly I'm driving a VW bus and need to get out and push.

[techntrek]

bumping...

[DiabloMatt]

bumping...

can you post up your original back up and your last tune written out of the "tunes" folder of your tool. let me take a look around.

[techntrek]

Will post when I can, currently on the road for 3 more weeks so online time is limited. I can confirm I see the same thing in the 87 tune, I had to switch to it a day or so ago as I approached the Rockies where 91+ octane isn't always available. I've actually experienced a slight mpg increase even with the hillier terrain and little noticeable loss in power (still using the highest octane which has been either 90 or 91). The computer still lets the speed drop off and stays in 3rd unless I force it to 2nd.

[retiredtechnician]

The 2010 Chevy 1500 Owner's Manual says "an overheat protection mode which alternates firing groups of cylinders helps prevent engine damage. In this mode, you will notice a loss in power and engine performance." Just throwing that out there.

Are you using the 'Tow' mode, 'Manual' mode, both, or neither? Do you have the 6-speed Hydra-Matic?

[techntrek]

I know about the various protections, like turning off the A/C once you hit a certain temp limit. I've hit that twice on this trip, both times the A/C came back on in a minute or two. No reduction in power warnings, that is a more severe overheating condition. This happens on every long pull when engine, radiator and oil temps are warm but not hot (I have an Aeroforce Interceptor to show various specs that aren't shown on the dash). Manually downshifting to 2nd shows there is some power in reserve once the rpms get over 4000.

I do think it is partly altitude related, since I'm now back down from 7000 feet to 2000 feet and it has downshifted to 2nd at around 45 mph several times - but not every time.

I am using tow mode and have the 6-speed.