No Good Answers in the Case of GMC's Slipping Transmission

Dear Car Talk:

I recently purchased a new 2020 GMC Sierra 1500 pickup truck. I have had GM products for over 50 years and am finally having problems.

My street has a slight incline. When I leave home in the morning and go uphill, my transmission slips quite a bit from first to second gear. This mostly happens when I first leave for the day. I don't notice it later on.

I took it to the dealer three times. The first time, they said my truck computer needs to learn my driving habits and adjust accordingly (what?). The next time, they changed some module or something and said that should take care of it. It didn't. Then, they said I have to drive another couple thousand miles for the computer to learn my driving habits again (what?).

The last time I took it in and told them I was not happy, they said they contacted the manufacturer or someone, and they were told that they know about the problem, and there is nothing they can do.

First of all, have you heard any such thing, a transmission learning a person's driving habits? I have always loved my GM cars and trucks, but what do I do about this? This truck cost me over $55,000, and I shouldn't have this kind of trouble. Thanks. -- Mark

I'm going to steal that line "Go drive it for a few thousand miles and then come back." They were hoping you'd be abducted by aliens during that time, and they'd never see you again.

Actually, modern transmissions do adjust to individual driving habits. The transmission computer uses a kind of crude artificial intelligence to learn whether you're a lead foot or a gentleman, and the shifts get adjusted, subtly, to accommodate your driving style. But the transmission doesn't have to "learn" not to slip.

Here's what we know about this transmission issue: When owners started complaining about "slipping" or slow shifts between first and second gear, GM discovered that there was a problem with a part called the "stator." That's not to be confused with the tall guy who pulls you over for doing 80 in a 65-mph zone.

The stator directs the flow of transmission fluid inside the torque converter. And if things aren't directed properly, you can have shifting problems. So GM made a change to the stator so fluid wouldn't drain out of it overnight. But then, owners started complaining about "harsh shifts" between first and second gear when the transmission was cold.

In the past, GM recommended a switch to a fully synthetic Mobil 1 transmission fluid, which they claim helps. But, after that, they gave up and switched to the answer you got; the mechanic's shrug. Essentially, "They all do that."

So I'd ask them if they'd be willing to try changing your transmission fluid, being sure to use the recommended fluid (Mobil 1 Synthetic LV ATF HP). But if that doesn't help, then you have a choice. You can either have a slipping problem or a harsh shifting problem.

If it were me, I'd take the slipping and leave it as is, because harsh shifts drive me nuts -- especially between first and second, which you feel every time you leave a traffic light. I don't think either problem will affect the life of the transmission in a meaningful way, if that helps you feel any better.

Yeah, after spending $55,000, I didn't think it would. Sorry, Mark.

Todays Car-o-Scope

What the stars say about your car for 8/3/2021
Whatever that noise is, it's going to be $200. If that's what it is.
Select your sign
  1. Aries
  2. Taurus
  3. Gemini
  4. Cancer
  5. Leo
  6. Virgo
  7. Libra
  8. Scorpio
  9. Sagittarius
  10. Capricorn
  11. Aquarius
  12. Pisces