94 Altima, need some help...

Hey everyone, I'm not a big car guy and I need some help identifying a problem that recently manifested. I drove home from school today, a drive that the car handled just fine in the past. When I started up my driveway, which is fairly steep, the engine wasn't getting enough power for some reason. It was going up to 2000+ RPM to get me up the driveway as fast as a snail. I went back to the car 10 minutes later to see if the problem was still there. It worked fine, took it around the block, and up the driveway no problem. This is the first car I've owned, but the fifth I've driven, never ran into a problem like this before. At first I thought the car was in neutral, but it wasn't falling out of gear or anything. Any tips would be greatly appriciated.