Very disappointed that the automatic transmission in my 2012 GMC Sierra began slipping after just 58k miles. This truck gets used pretty consistently, but at around 49k the transmission began slipping just a little, figured the truck was showing its age. Now the truck is not drivable, might as well put it in neutral! Is this something I can get repaired or is the whole transmission going to need replacing? I would like to fix this problem so it does not happen again.
The transmission in your truck has the updated 4L60 series with a heavier duty forward gears and thrust bearings so your transmission problem is most likely the torque converter or front pump failure. The clutch materials in an automatic transmission are very thin and if you have had slipping for over 10k miles you may have caused even more internal damage to other internal components. You will most likely need to have the transmission replaced or overhauled with a new torque converter. All the lines will need to be flushed out also to keep from contaminating the new or rebuilt transmission. Replacing the transmission with a remanufactured or a good used transmission with a warranty would be the recommendation I would give since the truck is under 10 years old and has low mileage.