Manual Transmission problems of the 2006 Mitsubishi Eclipse

4 months ago I had the slave cylinder leak onto my clutch causing the clutch to go out, they replaced it basically told me I have a new clutch. So recently I've been getting on the freeway in 5th 6th gear and the car is revving but not going, so I went back to the same dealer told them what's up and without even diagnosing the problem said I need a new clutch, I then reminded them I just had it replaced 4 months ago they tried to say it was for something else when in fact I remember him clearly saying you got a brand new clutch. Anyway I asked how much to fix it he said $1,400. 00 I then asked is it normal to have it go out so soon but he is still trying to convince me they just replaced the bearings on the clutch. Then asked if I drive it hard. Well I never race it I drive to and from work that's about it, OH and the car only has 16500 miles on it. I then called the finance department to find out about the warranty they said its not covered , I don't know im so mad about this I love the car but hate the people behind it!.