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Discussion Starter · #1 ·
Firstly, '05 Chevy Colorado, 2.8L Z85 4x4 (4L60E)

I've read through posts/forums for the last week and have seen many similar issues, but none that match my exact problem (or at least have described the same exact symptoms) so I'm going to post:

I'm having an intermittent but very predictable/repeatable issue where, only after the tranny warms up, I experience a downshift (from OD) on inclines... This is a new issue and has not occurred before since I've owned the truck, been driving the same exact way/route and the problem just manifested...
If I allow the RPMs to gradually hit 2500 on an incline (around 70/73-ish MPH) then the tranny will downshift and rev to 3,000 to 4,000 RPMs (at 65/70 MPH) and will not shift back once off the incline without pulling over and shutting off the truck to 'reset' I guess you'd call it.
Once 'reset' then I can drive normally as long as I don't allow the truck to gradually hit 2500 RPM on an incline. I can press the gas and accelerate up a hill, at the top of the hill I can release the gas and the tranny shifts back to OD just fine.... it's only when the exact gradual increase to 2500 RPM on an incline is seen that the problem occurs and remains until 'reset' by switching off the truck.
I drive out of state for work, a 4 hour drive. I’ve noticed the truck only does this during the first hour going to work, or the last hour coming home… which is during the very up/down (hills) portion of the trip. At first I thought it was only the 4th hour of the trip which made sense to me (fluid too hot or something similar) but I’ve also proven the truck can drive fine for the last three hours going to work when the roads are relatively flat… even standard bridges/overpasses don’t manifest the issue when infrequent.

Does this issue sound like a solenoid??
 

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Firstly, '05 Chevy Colorado, 2.8L Z85 4x4 (4L60E)

I've read through posts/forums for the last week and have seen many similar issues, but none that match my exact problem (or at least have described the same exact symptoms) so I'm going to post:

I'm having an intermittent but very predictable/repeatable issue where, only after the tranny warms up, I experience a downshift (from OD) on inclines... This is a new issue and has not occurred before since I've owned the truck, been driving the same exact way/route and the problem just manifested...
If I allow the RPMs to gradually hit 2500 on an incline (around 70/73-ish MPH) then the tranny will downshift and rev to 3,000 to 4,000 RPMs (at 65/70 MPH) and will not shift back once off the incline without pulling over and shutting off the truck to 'reset' I guess you'd call it.
Once 'reset' then I can drive normally as long as I don't allow the truck to gradually hit 2500 RPM on an incline. I can press the gas and accelerate up a hill, at the top of the hill I can release the gas and the tranny shifts back to OD just fine.... it's only when the exact gradual increase to 2500 RPM on an incline is seen that the problem occurs and remains until 'reset' by switching off the truck.
I drive out of state for work, a 4 hour drive. I’ve noticed the truck only does this during the first hour going to work, or the last hour coming home… which is during the very up/down (hills) portion of the trip. At first I thought it was only the 4th hour of the trip which made sense to me (fluid too hot or something similar) but I’ve also proven the truck can drive fine for the last three hours going to work when the roads are relatively flat… even standard bridges/overpasses don’t manifest the issue when infrequent.

Does this issue sound like a solenoid??
are you @don.wood ? look at this thread if not.... some kinda coincidence for sure!

http://coloradofans.com/forums/185-...sion/363713-overdrive-issues.html#post4554409
 

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Discussion Starter · #3 ·
no, not don.wood... and I did see that post, but again similar but not the same. Mine does it up a grade (more strain) not down a grade. also when mine does it I can pull over and come to a complete stop (but not shut off the ignition) and the truck will not get past 3rd on takeoff.... i have to come to a stop and turn off the ignition. (haven't tried it while rolling)
 

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no, not don.wood... and I did see that post, but again similar but not the same. Mine does it up a grade (more strain) not down a grade. also when mine does it I can pull over and come to a complete stop (but not shut off the ignition) and the truck will not get past 3rd on takeoff.... i have to come to a stop and turn off the ignition. (haven't tried it while rolling)
I saw your post and thought wow, that is strangely similar to his problem.
 

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Discussion Starter · #5 ·
I saw your post and thought wow, that is strangely similar to his problem.
yeah. I'm going to see if I can try and get a code pulled, only problem is that the tranny ONLY acts up on a particular stretch of interstate (hilly) either during the first hour of my 4 hour trip to work or the last hour on the way home. It does not do it ANY other time.... so I basically can only stop by a shop on my way home, otherwise everything is reset from shutting off the ignition.

I basically have one shot, once a week... if it even throws any codes at all. That's why I was hoping someone could chime in.
 

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Overdrive issue

I have an 05 Colorado that when cruising 60 - 70 going down a slight grade the overdrive disconnects, Have trouble getting it back unless I slow down to under 40 and speed up again then it will reconnect and sometimes it will take a long time or turn the ignition off and back on, that is instant. GM says because there is no engine light that it is normal. I've been driving for 60 years and that is not right. Does anyone have the problem? This only happens when we have no load pull or no downward hold back. When I am just at the middle of power or no power is when it will come out. GM has scanned and reprogramed the truck and didn't help One dealer tells me just drive it. I drive from Connecticut to New Hampshire and I can tell when it will come out of OD by looking at the road. It will come out 20 + times in that distance. I have to get on and off the throttle in order to keep it locked up.
 

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Discussion Starter · #7 ·
yeah. I'm going to see if I can try and get a code pulled, only problem is that the tranny ONLY acts up on a particular stretch of interstate (hilly) either during the first hour of my 4 hour trip to work or the last hour on the way home. It does not do it ANY other time.... so I basically can only stop by a shop on my way home, otherwise everything is reset from shutting off the ignition.

I basically have one shot, once a week... if it even throws any codes at all. That's why I was hoping someone could chime in.
UPDATE:
I installed the new MAP sensor and 'master' solenoid kit (included A and B shift, 3/2 downshift, EPC, SWM, Manifold Pressure Switch, and TCC/lock up w/ wiring harness) $150 kit on EBAY.... between the 8 parts (fingers crossed) one of them seems to have fixed the problem. I've made 2 trips down the stretch of road that always gives me trouble, with no issues noted. Just thought I'd share in case someone is having similar issues.
 

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UPDATE:
I installed the new MAP sensor and 'master' solenoid kit (included A and B shift, 3/2 downshift, EPC, SWM, Manifold Pressure Switch, and TCC/lock up w/ wiring harness) $150 kit on EBAY.... between the 8 parts (fingers crossed) one of them seems to have fixed the problem. I've made 2 trips down the stretch of road that always gives me trouble, with no issues noted. Just thought I'd share in case someone is having similar issues.

@don.wood
 

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UPDATE:
I installed the new MAP sensor and 'master' solenoid kit (included A and B shift, 3/2 downshift, EPC, SWM, Manifold Pressure Switch, and TCC/lock up w/ wiring harness) $150 kit on EBAY.... between the 8 parts (fingers crossed) one of them seems to have fixed the problem. I've made 2 trips down the stretch of road that always gives me trouble, with no issues noted. Just thought I'd share in case someone is having similar issues.

@don.wood
 
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