2000 Dodge Durango Have a Transmission leak

I took my car for a normal oil change this past week and suddenly the mechanic at WalMart informed me you have a massice transmission leak that is leaking into your transmission drip pan. I can't seem to find the leak. However, the tech stated that it's a big enough leak that it forms little dripplets off the transmission and falls into the drip pan. However, I had the car site for 2 days before taking it for an oil change and no signs of oil on our driveway. How can I fix the leak if we have one? ANd is it the tranny seal or what steps need to be done to verify this information? Truck shifts and drived perfect, only thing I notice is when you start out and drive slow it seems not to grab very fast, but then again I'm use to mor trorque and accerlaration from GMC Trucks and Vans.