Ok, I have allot to say about this. First off, it is a misconception that turtles are lazy or slow. Second Red eared sliders do bask allot. They can spend many hours of the day out of the water with out any ill effects. They are only semi aquatic turtles. Your turtle is probably just warming itself up. Particularly if you do not have a heater in the tank. Third, if you are concerned for your turtle's health, then you need to take it to a vet. A vet that deals with reptiles is going to know way more about turtles than the pet shop you got it from. I know this because I also own a red eared slider. Also, if the comment you left Deuteronomy 27 is true, and you live in the united states, do not tell anyone else about it because unless your friend has a license to breed these animals, hatching them is illegal. So, just don't say any more about that part.
All turtles are lazy and slow - this is normal - but check just in case - go to the place where you bought him and ask them if there is anything wrong with your turtle. It's hard to tell a healthy one from a sick one.