I bought in January 2014 Dodge Durango Limited model with six-cylinder 3.6 engine and eight-speed automatic transmission.

I noticed while driving the car in the highways speed from 125 KM to 140 KM and above that the transmission does not last on the eighth speed and I was back to the speed of the seventh. This makes the RPM indicator higher up to 3,000 RPM in speed seven but in eighth speed up to 2500 cycle and this make greater fuel consumption and increase engine sound.

I have tried every way to re-transmission speed eighth tried to shift manually but it good back to seventh speed , I took the car to the dealer in the region and has a technician experimenting the car with me and he noticed the same problem then he told me that this is not a problem and all cars of this type of hands the same holidays. I'm not convinced of his explanation and I want you to help me solve this problem and if there is no solution I do not want this car.