transmission problem or not?

We test drove a 2011 Nissan Altima SL yesterday and like the car. However, there seemed to be a problem with the transmission at high speeds. When you accelerate from say 60 to 80 mph and then back off to maintain constant speed at 80, the transmission does not shift up and the RPMs remain at 5 or 6K. We had to transfer over to the manual mode and up shift in order to get the rpms down. The salesman said its because the transmission is computerized and doesn't know your driving habits yet, but it will adjust. And maybe the old lady that owned it just didn't take it on the highway. Despite the reassurance, I'm concerned and would like the opinion of a Nissan mechanic. Does it sound like there is something wrong with the transmission or is there merit to the computer explanation?

Thanks

Walk away!