If you're looking for a used Tahoe, it's important to be aware of the model years that have been known to have transmission problems. The most common issues seem to crop up in the 2007 and 2008 models, although there have also been reports of problems in the 2009 and 2010 model years.
One of the main issues seems to be with the Tahoe's 4-speed automatic transmission. Some owners report that their transmission starts slipping or becoming less responsive after just a few thousand miles. In some cases, this can lead to complete failure of the transmission, which is a very costly repair.
Another issue that has been reported is with the transfer case. This is what transfers power from the engine to the wheels, and some owners have reported problems with it leaking fluid or becoming completely detached from the vehicle. Again, this is a very expensive repair if it needs to be done by a professional.
If you're considering buying a used Tahoe, it's definitely worth doing your research first and making sure you're aware of any potential issues that could crop up down the road. With proper care and maintenance, though, these issues can usually be avoided altogether.