Hope to Purchase 2011 Prius-Acceleration Question

Took a 2011 with 99k miles on a test drive on the highway. Prius is priced at $6800. Loved the car, however, I noticed that when we got up to 60 mph, I would continue to press on the accelerator and would have to press a few seconds longer (than previously) for the mph to increase to 61, 62 and so on-seemed like an odd delay of some kind. I assumed it's a transmission or engine problem, but I am far from a car expert and wanted to be sure this is NOT typical of these types of cars. Also, do most owners have to bring these cars to dealerships for maintenance or are typical mechanics equipped to work on these cars. Any help would be appreciated. Thanks