What is considered high mileage on used Hybrid GMC Yukon? I am considering the purchase of a used Hybrid GMC Yukon or Chevrolet Tahoe. Is 125,000 high mileage for a Hybrid, like a standard gasoline V8 engine in these suvs?
I don't have specific experience with GMC Yukon or Chevrolet Tahoe hybrids, but I do know quite a bit about Toyota hybrids.
Basically, the transmission is nearly indestructible, being based on an electric CVT approach. If you ever manage to destroy it, replacement of the transmission with its two integrated electric motors costs less than replacement of a conventional automatic (or manual) transmission. If a single electric motor fails, you don't replace it, you replace the entire cheap transmission!
However, the transmission in GMC Yukon hybrids seems different, being partially based on automatic transmission technology and not just planetary electric CVT technology. So, the risks in purchasing GMC Yukon hybrid are larger than the risks of purchasing a Toyota hybrid, being probably similar to the risks of purchasing a used automatic transmission vehicle.
The inverter can in theory fail, containing lots of power electronics. However, inverters are used in many other environments like locomotives, elevators, etc. and typically they are expected to have quite long service lifes, so I don't believe inverter failure is the largest thing to worry about. If there ever has been a cooling circuit leak (inverters are water-cooled, or more accurately coolant-cooled), I would worry about inverter failure.
That leaves the battery. Toyota hybrids have extremely low battery failure rate, and Consumer Reports has tested the mileage of 200 000 mile driven Prius (spoiler: the mileage was just fine). But, Honda hybrids have had higher rates of battery failure due to imperfect charging algorithms when subjected to certain driving patterns. Basically, the chances of NiMH battery lasting for the expected service life depend on the charging algorithm.
Where I live, Toyota offers 350 000 kilometer warranty for the hybrid battery. They wouldn't offer this warranty if they didn't trust in the technology.
I would therefore treat purchase of a high-mileage used hybrid like the purchase of any high-mileage used car. I don't see how the hybrid technology would make it more risky. In my opinion, the long-term durability of these components should make the purchase less risky.
For any used car purchase, you should know what the weaknesses of the particular model you're planning to purchase are. This applies to hybrids, but hybrids have far less transmission related weaknesses.