I have a 2001 chevy S10 pickup with a 4 cyl. engine and auto transmission. I’ve had this problem since I bought it used in 2006. What happens is when I am driving on the highway (55mph and up), there are times when the engine will downshift from 4th to 3rd gear while I am driving at a constant speed. I’m not pressing on the gas to accelerate faster and it happens even when I am driving on a flat road. This usually happens during the hotter months, from about April to October and hardly happens if at all during the colder months of winter making me think it is a temperature related problem.
What I’ve noticed over the years is that it happens more frequently if I drive in the city first (doing a lot of stopping and going) and then get on the highway. I’ve noticed it more when I am driving on the highway and let’s say for instance the car in front of me starts to slow down, and when I start to lift my foot off the gas, that’s when it will downshift from 4th to 3rd. I usually have to let my foot completely off the gas so that it shifts back up to 4th and then start to press on the gas again. If I have been driving for a while, it keeps happening, and there have been times where I drove slower on the highway to keep it form acting up so frequently.
I took it to a Chevy dealer this past summer to have it looked at. The repair man said that he did not know what would be causing it and that they couldn’t replicate the problem so I took it on a drive, with him riding with me, and got it to act up once on the drive. He observed what it was doing and would talk to another mechanic about it. He later concluded that it was just how the truck operates when driving at high speeds like that with a hot engine. I told him that I am mainly concerned about over-reving my engine, but he said that is not a concern. However, neither him nor anybody that I have talked to has ever heard about this happening to any other vehicles. I even had the transmission fluid replaced two summers ago, but it didn’t seem to make an impact.
Is the Chevy mechanic right about it just being a normal operating feature of the engine/vehicle, or could it be something else?